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Cycad

Cycad

Cycadaceae cycas family
Stangeriaceae stangeria family
Zamiaceae zamia family Cycads are an ancient group of seed plants characterized by a large crown of compound leaves and a stout trunk. They are evergreen, gymnospermous, dioecious plants having large pinnately compound leaves. They are frequently confused with and mistaken for palms or ferns, but are unrelated to either, belonging to the division Cycadophyta.

Introduction & overview

Cycads are found across much of the subtropical and tropical parts of the world. They are found in South and Central America (where the greatest diversity occurs), Australia, the Pacific Islands, Japan, China, India, Madagascar, and southern and tropical Africa, where at least 65 species occur. Some are renowned for survival in harsh semi-desert climates, and can grow in sand or even on rock. They are able to grow in full sun or shade, and some are salt tolerant. Though they are a minor component of the plant kingdom today, during the Jurassic period they were extremely common. Sago is made from these plants. They are very specialized pollinators and have been reported to fix nitrogen in association with a cyanobacterium living in the roots. This blue-green algae produces a neurotoxin called BMAA that is found in the fruits of cycads. fruit

Taxonomy

There are 289 species, 11 genera and 3 families of cycads. The classification below, proposed by Dennis Stevenson in 1990, is based upon a hierarchical structure based on cladistic analyses of morphological, anatomical, karyological, physiological and phytochemical data.

Order Cycadales

;Suborder Cycadineae :Family Cycadaceae ::Subfamily Cycadoideae :::::Cycas. About 90 species in the Old World from Africa east to southern Japan, Australia and the western Pacific Ocean islands; type: C. circinalis L.; see also C. pruinosa and C. revoluta ;Suborder Zamiineae :Family Stangeriaceae ::Subfamily Stangerioideae :::::Stangeria. One species in southern Africa; type: S. eriopus (Kunze) Baillon ::Subfamily Bowenioideae :::::Bowenia. Three species in Queensland, Australia; type: B. spectabilis Hook. ex Hook. f. :Family Zamiaceae ::Subfamily Encephalartoideae :::Tribe Diooeae :::::Dioon. Ten species in Mexico and Central America; type: D. edule Lindley :::Tribe Encephalarteae ::::Subtribe Encephalartinae :::::Encephalartos. About 60 species in southeast Africa; type: E. friderici-guilielmi Lehmann, E. transvenosus (Modjadji cycad) ::::Subtribe Macrozamiinae :::::Macrozamia. About 30 species in Australia; type: M. riedlei (Fischer ex Gaudichaud) C.A. Gardner :::::Lepidozamia. Two species in eastern Australia; type: L. peroffskyana Regel ::Subfamily Zamioideae :::Tribe Ceratozamieae :::::Ceratozamia. Twelve species in southern Mexico and Central America; type: C. mexicana Brongn. :::Tribe Zamieae ::::Subtribe Microcycadinae :::::Microcycas. One species in Cuba; type: M. calocoma (Miquel) A. DC. ::::Subtribe Zamiinae :::::Chigua. Two species in Colombia; type: C. restrepoi E. Stevenson :::::Zamia. About 60 species in the New World from Georgia, USA south to Bolivia; type: Z. pumila L.; see also Z. furfuracea

History

Modern knowledge about Cycads began in the 9th century with the discovery by two Arab naturalists that the genus Cycas was used as a source of flour in India. Later, in the 16th century, Antonio Pigafetta, Fernao Lopez de Castanheda and Francis Drake found Cycas plants in the Moluccas, where the seeds were eaten. The first report of cycads in the New World was by Giovanni Lerio in his 1576 trip to Brazil, where he observed a plant named ayrius by the indigenous people; this species is now classified in the genus Zamia. Cycads belonging to the genus Encepharlartos were first described by Johann Georg Christian Lehmann in 1834. The name is derived from the Greek articles "en", meaning "in", "cephale", meaning "head", and "artos", meaning "bread". The generic name refers to the starch obtained from the stems which was used as food by some indigenous tribes. Throughout the 18th-19th centuries, discoveries of several species were reported by numerous naturalist researchers and discoverers traveling throughout the world. One of the most notable researchers of cycads was American botanist C.J. Chamberlain whose work is noteworthy for the quantity of data and the novelty of his approach to studying cycads. His 15 years of travel throughout Africa, the Americas and Australia to observe cycads in their natural habitat resulted in his 1919 publication of The Living Cycads which remains a flowing and data rich volume, and which remains current in its synthesis of taxonomy, morphology and reproductive biology of cycads, most of which was obtained from his original research. His 1940's monograph on the Cycadales, though never published (most likely because of his death) was never used by botanists. There are no other complete works on the cycads.

Conservation

monograph In recent years, many cycads have been dwindling in numbers and may face risk of extinction because of theft and unscrupulous collection from their natural habitats, as well as from habitat destruction. All cycads are in the CITES appendix appearing under the heading Plant Kingdom and under three family names: Cycadaceae, Stangeriaceae and Zamiaceae. All cycads are CITES APPENDIX II except the following, in APPENDIX I:
- Cycas beddomei
- Stangeria eriopus
- All Ceratozamia
- All Chigua
- All Encephalartos
- Microcycas calocoma Cycad seeds are not CITES regulated. APPENDIX I seeds are treated the same as the plants. A 1997 the International Union for the Conservation of Nature and Natural Resources (IUCN), now known as the World Conservation Union, reported a list of over 150 threatened Cycad Species throughout the world that are indeterminate, rare, vulnerable, endangered or extinct.

Horticulture

extinct Cycads can be cut up into pieces to make new plants, although the most environmentally responsible method is by direct planting of the seeds. Propagation by seeds is the preferred method of growth, and two unique risks to their germination exist. One is that the seeds have no dormancy, so that the embryo is biologically required to maintain growth and development, which means if the seed dries out, it dies. The second is that the emerging radicle and embryo can be very susceptible to fungal diseases in its early stages when in unhygienic or excessively wet conditions. Thus, many cycad growers pre-germinate the seeds in moist, sterile mediums such as vermiculite or perlite. However pre-germination is not necessary, and many report success by directly planting the seeds in regular potting soil. As with many plants, a combination of well-drained soil, sunlight, water and nutrients will help it to prosper. Although, because of their hardy nature cycads do not necessarily require the most tender or careful treatment, they can grow in almost any medium, including soil-less ones. One of the most common cause of cycad death is from rotting stems and roots due to over-watering. Some insects, particularly scale insects, some weevils and chewing insects can damage cycads, though the pests are susceptible to insecticides such as the horticulture soluble oil white oil. Sometimes bacterial preparations may be used to control insect infestation on cycads. However, when some of the mature plants prepare for reproduction, the presence of weevils have been shown to help accomplish pollination. While the cycads have a reputation of slow growth, it is not always well-founded and some actually grow quite fast, achieving reproductive maturity in 2 to 3 years (as with some Zamia species), while others in 15 years (as with some Cycas, Australian Macrozamia and Lepidozamia).

References

- A Historical Perspective on Cycads from Antiquity to the Present, by Paolo De Luca (Dipartimento di Biologia vegetale and Orto Botanico, Universita di Napoli, via Foria 223, 80139 Napoli, Italia). A historical perspective on cycads from antiquity to the present.
- Memoirs of the New York Botanical Garden 57: 1-7. 1990. A brief survey of the history of cycads in various cultures.
- Jones, David L. 2002. Cycads of the World. Smithsonian Institution Press. ISBN 1-56098-220-9. Also published in 2002 as: Cycads of the World: Ancient Plants in Today's Landscape. Reed New Holland, Sydney. ISBN 1-876334-69-X

External links

- [http://plantnet.rbgsyd.gov.au/PlantNet/cycad/ The Cycad Pages (at RBG Sydney, Australia)]
- [http://www.conifers.org/cycadales.htm Gymnosperm Database: Cycads]
- [http://www.fairchildgarden.org/horticulture/n_collections.html Fairchild Tropical Botanic Garden- one of the largest collection of cycads in the world in Florida, U.S.A.]
- [http://www.pacsoa.org.au/ Palm and Cycad Societies of Australia (PACSOA)]
- [http://www.cycadsociety.org/index.html The Cycad Society of South Africa]
- [http://academic.reed.edu/biology/Nitrogen/Nfix1.html Cycad nitrogen fixation]
- [http://plantnet.rbgsyd.gov.au/PlantNet/cycad/toxic.html Cycad toxicity]
- [http://www.nytimes.com/2005/08/28/magazine/28CYCADS.html?8hpib=&pagewanted=print The Cult of the Cycads], New York Times Magazine article on cycad collectorship and cycad smuggling Category:Cycads ja:ソテツ類

Cycadaceae

Cycas aculeata
Cycas angulata
Cycas apoa
Cycas arenicola
Cycas armstrongii
Cycas arnhemica
Cycas badensis
Cycas balansae
Cycas basaltica
Cycas beddomei
Cycas bifida
Cycas bougainvilleana
Cycas brachycantha
Cycas brunnea
Cycas cairnsiana
Cycas calcicola
Cycas campestris
Cycas candida
Cycas canalis
Cycas chamaoensis
Cycas changjiangensis
Cycas chevalieri
Cycas circinalis
Cycas clivicola
Cycas collina
Cycas condaoensis
Cycas conferta
Cycas couttsiana
Cycas curranii
Cycas debaoensis
Cycas desolata
Cycas diannanensis
Cycas dolichophylla
Cycas edentata
Cycas elephantipes
Cycas elongata
Cycas falcata
Cycas fairylakea
Cycas ferruginea
Cycas fugax
Cycas furfuracea
Cycas guizhouensis
Cycas hainanensis
Cycas hoabinhensis
Cycas hongheensis
Cycas inermis
Cycas javana
Cycas lanepoolei
Cycas lindstromii
Cycas litoralis
Cycas maconochiei
Cycas macrocarpa
Cycas media
Cycas megacarpa
Cycas micholitzii
Cycas micronesica
Cycas multipinnata
Cycas nathorstii
Cycas nongnoochiae
Cycas ophiolitica
Cycas orientis
Cycas pachypoda
Cycas panzhihuaensis
Cycas papuana
Cycas pectinata
Cycas petraea
Cycas platyphylla
Cycas pranburiensis
Cycas pruinosa
Cycas revoluta
Cycas riuminiana
Cycas rumphii
Cycas schumanniana
Cycas scratchleyana
Cycas seemannii
Cycas segmentifida
Cycas semota
Cycas sexseminifera
Cycas siamensis
Cycas silvestris
Cycas simplicipinna
Cycas spherica
Cycas szechuanensis
Cycas taitungensis
Cycas taiwaniana
Cycas tanqingii
Cycas tansachana
Cycas thouarsii
Cycas tropophylla
Cycas tuckeri
Cycas wadei
Cycas xipholepis
Cycas yorkiana
Cycas yunnanensis
Cycas zeylanica Cycas is a genus of cycads, the only genus in the Cycadaceae. About 95 species are currently accepted, native to southeast Asia, east Africa and Australasia; the northernmost at 31°N in southern Japan, the southernmost at 26°S in southeast Queensland, Australia. Category:Cycads ja:ソテツ

Stangeriaceae

Bowenia
Stangeria Stangeriaceae is the smallest family of cycads, both in number of living and fossil species. The family contains only two living genera, Stangeria and Bowenia, though the latter genus has been recommended for placement in a separate family by itself. The family is recognized by having vascularized stipules, and by lacking cataphylls, or producing them irregularly. These unusual characters led to the original description of Stangeria as a fern, and it was only when seeds were later produced on the plant that its true affinities were realized. Though today the family occurs only in South Africa and Queensland, Australia, fossils are known from Jurassic sediments in the British Isles. Recent cladistic studies suggest that the fossil taxon Mesodescolea may also have affinities with the Stangeriaceae. This highly lobed fossil leaf from the Lower Cretaceous has only been found in Argentina. Category:Cycads

Zamiaceae

See text The Zamiaceae are a family of cycads that are superficially palm or fern-like. They are divided into two subfamilies with eight genera and about 150 species in the tropical and warm temperate regions of Africa, Australia and North and South America. The Zamiaceae are perennial, evergreen, and dioecious. They have subterranean to tall and erect, usually unbranched, cylindrical stems, and stems clad with persistent leaf bases (in Australian genera). Their leaves are simply pinnate, spirally arranged, and interspersed with cataphylls. The leaflets are sometimes dichotomously divided. The leaflets occur with several sub-parallel, dichotomously-branching longitudinal veins; they lack a mid rib. Stomata occur either on both surfaces or undersurface only. Their roots have small secondary roots. The coral-like roots develop at the base of the stem at or below the soil surface. Male and female sporophylls are spirally aggregated into determinate cones that grow along the axis. Female sporophylls are simple, appearing peltate, with a barren stipe and an expanded and thickened lamina with 2 (rarely 3 or more) sessile ovules inserted on the inner (axis facing) surface and directed inward. The seeds are angular, with the inner coat hardened and the outer coat fleshy. They are often brightly colored, with 2 cotyledons. One subfamily, the Encephalartoideae, is characterized by spirally arranged sporophylls (rather than spirally orthostichous), non-articulate leaflets and persistent leaf bases. It is represented in Australia, with two genera and 40 species.

Genera

- Subfamily Encephalartoideae
- Chigua
- Dioon
- Encephalartos, including the Modjadji cycad
- Lepidozamia
- Subfamily Zamioideae
- Macrozamia
- Ceratozamia
- Microcycas
- Zamia Some classifications also place the genus Bowenia in the Zamiaceae. As with all cycads, members of the Zamiaceae are poisonous, producing poisonous glycosides known as cycasins.

References

- [http://plantnet.rbgsyd.gov.au/PlantNet/cycad/zamiacea.html The Cycad Pages: Zamiaceae]
- [http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10958 Flora of North America]
- [http://www.nybg.org/bsci/hcol/vasc/Zamiaceae.html New York Botanical Garden: Vascular Plant Type Catalog, some Zamiaceae genera and species.] Category:Cycads

Plants

- Land plants (embryophytes)
- Non-vascular plants (bryophytes)
- Marchantiophyta - liverworts
- Anthocerotophyta - hornworts
- Bryophyta - mosses
- Vascular plants (tracheophytes)
- Lycopodiophyta - clubmosses
- Equisetophyta - horsetails
- Pteridophyta - "true" ferns
- Psilotophyta - whisk ferns
- Ophioglossophyta - adderstongues
- Seed plants (spermatophytes)
- †Pteridospermatophyta - seed ferns
- Pinophyta - conifers
- Cycadophyta - cycads
- Ginkgophyta - ginkgo
- Gnetophyta - gnetae
- Magnoliophyta - flowering plants Magnoliophyta Plants are a major group of living things (about 300,000 species), including familiar organisms such as trees, flowers, herbs, and ferns. Aristotle divided all living things between plants, which generally do not move or have sensory organs, and animals. In Linnaeus' system, these became the Kingdoms Vegetabilia (later Plantae) and Animalia. Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these are still often considered plants in many contexts. Indeed, any attempt to match "plant" with a single taxon is doomed to fail, because plant is a vaguely defined concept unrelated to the presumed phylogenic concepts on which modern taxonomy is based.

Embryophytes

:See main article at Embryophytes Most familiar are the multicellular land plants, called embryophytes. They include the vascular plants, plants with full systems of leaves, stems, and roots. They also include a few of their close relatives, often called bryophytes, of which mosses and liverworts are the most common. All of these plants have eukaryotic cells with cell walls composed of cellulose, and most obtain their energy through photosynthesis, using light and carbon dioxide to synthesize food. About three hundred plant species do not photosynthesize but are parasites on other species of photosynthetic plants. Plants are distinguished from green algae, from which they evolved, by having specialized reproductive organs protected by non-reproductive tissues. Bryophytes first appeared during the early Palaeozoic. They can only survive where moisture is available for significant periods, although some species are desiccation tolerant. Most species of bryophyte remain small throughout their life-cycle. This involves an alternation between two generations: a haploid stage, called the gametophyte, and a diploid stage, called the sporophyte. The sporophyte is short-lived and remains dependent on its parent gametophyte. Vascular plants first appeared during the Silurian period, and by the Devonian had diversified and spread into many different land environments. They have a number of adaptations that allowed them to overcome the limitations of the bryophytes. These include a cuticle resistant to desiccation, and vascular tissues which transport water throughout the organism. In most the sporophyte acts as a separate individual, while the gametophyte remains small. Devonians (Pteridophyta) more closely allied to seed plants than they are to clubmosses (Lycopodiophyta)]] The first primitive seed plants, Pteridosperms (seed ferns) and Cordaites, both groups now extinct, appeared in the late Devonian and diversified through the Carboniferous, with further evolution through the Permian and Triassic periods. In these the gametophyte stage is completely reduced, and the sporophyte begins life inside an enclosure called a seed, which develops while on the parent plant, and with fertilisation by means of pollen grains. Whereas other vascular plants, such as ferns, reproduce by means of spores and so need moisture to develop, some seed plants can survive and reproduce in extremely arid conditions. Early seed plants are referred to as gymnosperms (naked seeds), as the seed embryo is not enclosed in a protective structure at pollination, with the pollen landing directly on the embryo. Four surviving groups remain widespread now, particularly the conifers, which are dominant trees in several biomes. The angiosperms, comprising the flowering plants, were the last major group of plants to appear, emerging from within the gymnosperms during the Jurassic and diversifying rapidly during the Cretaceous. These differ in that the seed embryo is enclosed, so the pollen has to grow a tube to penetrate the protective seed coat; they are the predominant group of flora in most biomes today.

Algae and Fungi

The algae comprise several different groups of organisms that produce energy through photosynthesis. However, they are not classified within the kingdom plantae but in the kingdom protista instead. The most conspicuous are the seaweeds, multicellular algae that often closely resemble terrestrial plants, but as stated above are not plants, found among the green, red, and brown algae. These and other algal groups also include various single-celled creatures and forms that are simple collections of cells, without differentiated tissues. Many can move about, and some have even lost their ability to photosynthesize; when first discovered, these were considered as both plants and animals. Now they are considered neither, but protists. The embryophytes developed from green algae; the two are collectively referred to as the green plants or Viridiplantae. The kingdom Plantae is now usually taken to mean this monophyletic group, as shown above. With a few exceptions among the green algae, all such forms have cell walls containing cellulose and chloroplasts containing chlorophylls a and b, and store food in the form of starch. They undergo closed mitosis without centrioles, and typically have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria. The same is true of the red algae, and the two groups are generally believed to have a common origin. In contrast, most other algae have chloroplasts with three or four membranes. They are not in general close relatives of the green plants, acquiring chloroplasts separately from ingested or symbiotic green and red algae. Unlike embryophytes and algae, fungi are not photosynthetic, but are saprophytes: they obtain their food by breaking down and absorbing surrounding materials. Most fungi are formed by microscopic tubes called hyphae, which may or may not be divided into cells but contain eukaryotic nuclei. Fruiting bodies, of which mushrooms are the most familiar, are actually only the reproductive structures of fungi. They are not related to any of the photosynthetic groups, but are close relatives of animals. Therefore, fungus has a kingdom of its own.

Importance

The photosynthesis and carbon fixation conducted by land plants and algae are the ultimate source of energy and organic material in nearly all habitats. These processes also radically changed the composition of the Earth's atmosphere, which as a result contains a large proportion of oxygen. Animals and most other organisms are aerobic, relying on oxygen; those that do not are confined to relatively few, anaerobic environments. Much of human nutrition depends on cereals. Other plants that are eaten include fruits, vegetables, herbs, and spices. Some vascular plants, referred to as trees and shrubs, produce woody stems and are an important source of building material. A number of plants are used decoratively, including a variety of flowers.

Growth

It is a common misconception that most of the solid material in a plant is taken from the soil, when in fact almost all of it is actually taken from the air. Through a process known as photosynthesis, plants use the energy in sunlight to convert carbon dioxide from the air into simple sugars. These sugars are then used as building blocks and form the main structural component of the plant. Plants rely on soil primarily for water (in quantitative terms), but also obtain nitrogen, phosphorus and other crucial nutrients. phosphorus Simple plants like algae may have short life spans as individuals, but their populations are commonly seasonal. Other plants may be organized according to their seasonal growth pattern:
- Annual: live and reproduce within one growing season.
- Biennial: live for two growing seasons; usually reproduce in second year.
- Perennial: live for many growing seasons; continue to reproduce once mature. Among the vascular plants, perennials include both evergreens that keep their leaves the entire year, and deciduous plants which lose their leaves for some part. In temperate and boreal climates, they generally lose their leaves during the winter; many tropical plants lose their leaves during the dry season. The growth rate of plants is extremely variable. Some mosses grow less than 0.001 mm/h, while most trees grow 0.025-0.250 mm/h. Some climbing species, such as kudzu, which do not need to produce thick supportive tissue, may grow up to 12.5 mm/h.

Fossils

Plant fossils include roots, wood, leaves, seeds, fruit, pollen, spores, phytoliths, and amber (the fossilized resin produced by some plants). Fossil land plants are recorded in terrestrial, lacustrine, fluvial and nearshore marine sediments. Pollen, spores and algae (dinoflagellates and acritarchs) are used for dating sedimentary rock sequences. The remains of fossil plants are not as common as fossil animals, although plant fossils are locally abundant in many regions worldwide. Early fossils of these ancient plants show the individual cells within the plant tissue. The Devonian period also saw the evolution of what many believe to be the first modern tree, Archaeopteris. This fern-like tree combined a woody trunk with the fronds of a fern, but produced no seeds. Archaeopteris The Coal Measures are a major source of Palaeozoic plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect; coal itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the Fossil Forest at Victoria Park in Glasgow, Scotland, the stumps of Lepidodendron trees are found in their original growth positions. The fossilized remains of conifer and angiosperm roots, stems and branches may be locally abundant in lake and inshore sedimentary rocks from the Mesozoic and Caenozoic eras. Sequoia and its allies, magnolia, oak, and palms are often found. Petrified wood is common in some parts of the world, and is most frequently found in arid or desert areas were it is more readily exposed by erosion. Petrified wood is often heavily silicified (the organic material replaced by silicon dioxide), and the impregnated tissue is often preserved in fine detail. Such specimens may be cut and polished using lapidary equipment. Fossil forests of petrified wood have been found in all continents. Fossils of seed ferns such as Glossopteris are widely distributed throughout several continents of the southern hemisphere, a fact that gave support to Alfred Wegener's early ideas regarding Continental drift theory.

Distribution

References and further reading

- Kenrick, Paul & Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D. C.: Smithsonian Institution Press. ISBN 1-56098-730-8.
- Raven, Peter H., Evert, Ray F., & Eichhorn, Susan E. (2005). Biology of Plants (7th ed.). New York: W. H. Freeman and Company. ISBN 0-7167-1007-2.
- Taylor, Thomas N. & Taylor, Edith L. (1993). The Biology and Evolution of Fossil Plants. Englewood Cliffs, NJ: Prentice Hall. ISBN 0-13-651589-4.

External links

- [http://tolweb.org/tree?group=Green_plants&contgroup=Eukaryotes Tree of Life]
- Chaw, S.-M. et al. [http://mbe.library.arizona.edu/data/1997/1401/7chaw.pdf Molecular Phylogeny of Extant Gymnosperms and Seed Plant Evolution: Analysis of Nuclear 18s rRNA Sequences (pdf file)] Molec. Biol. Evol. 14 (1): 56-68. 1997.
- [http://florabase.calm.wa.gov.au/phylogeny/cronq88.html Interactive Cronquist classification]

Botanical and vegetation databases

- [http://www.efloras.org/index.aspx e-Floras (Flora of China, Flora of North America and others)]
- [http://plants.usda.gov/ United States of America]
- [http://rbg-web2.rbge.org.uk/FE/fe.html Flora Europaea]
- [http://www.anbg.gov.au/cpbr/databases/ Australia]
- [http://davesgarden.com/pdb/ 'Dave's Garden' horticultural plant database]
- [http://www.chilebosque.cl Chilean plants at Chilebosque] Category:Plants Category:Plant_taxonomy zh-min-nan:Si̍t-bu̍t ko:식물 ms:Tumbuhan ja:植物 simple:Plant th:พืช

Leaf

:This article is about the leaf, a plant organ. See Leaf (disambiguation) for other meanings. ---- In botany, a leaf is an above-ground plant organ specialized for photosynthesis. For this purpose, a leaf is typically flat (laminar) and thin, to expose the chloroplast containing cells (chlorenchyma tissue) to light over a broad area, and to allow light to penetrate fully into the tissues. Leaves are also the sites in most plants where respiration, transpiration, and guttation take place. Leaves can store food and water, and are modified in some plants for other purposes. The comparable structures of ferns are correctly referred to as fronds. frond frond frond

Leaf anatomy

A structurally complete leaf of an angiosperm consists of a petiole (leaf stem), a lamina (leaf blade), and stipules (small processes located to either side of the base of the petiole). The point at which the petiole attaches to the stem is called the leaf axil. Not every species produces leaves with all of these structural parts. In some species, paired stipules are not obvious or are absent altogether; a petiole may be absent; or the blade may not be laminar (flattened). The tremendous variety shown in leaf structure (anatomy) from species to species is presented in detail below under Leaf types, arrangements, and forms. A leaf is considered to be a plant organ, typically consisting of the following tissues: # An epidermis that covers the upper and lower surfaces # An interior chlorenchyma called the mesophyll # An arrangement of veins (the vascular tissue). stipule

Epidermis

The epidermis is the outer multi-layered group of cells covering the leaf. It forms the boundary between the plant and the external world. The epidermis serves several functions: protection against water loss, regulation of gas exchange, secretion of metabolic compounds, and (in some species) absorption of water. Most leaves show dorsoventral anatomy: the upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions. The epidermis is usually transparent (epidermal cells lack chloroplasts) and coated on the outer side with a waxy cuticle that prevents water loss. The cuticle may be thinner on the lower epidermis than on the upper epidermis; and is thicker on leaves from dry climates as compared with those from wet climates. The epidermis tissue includes several differentiated cell types: epidermal cells, guard cells, subsidiary cells, and epidermal hairs (trichomes). The epidermal cells are the most numerous, largest, and least specialized. These are typically more elongated in the leaves of monocots than in those of dicots. The epidermis is covered with pores called stomata (sing., stoma), part of a stoma complex consisting of a pore surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts. The stoma complex regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Typically, the stomata are more numerous over the abaxial (lower) epidermis than the (adaxial) upper epidermis. Trichomes or hairs grow out from the epidermis in many species.

Mesophyll

Most of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma (ground tissue) or chlorenchyma tissue called the mesophyll (= middle leaf). This "assimilation tissue" is the primary location of photosynthesis in the plant. The products of photosynthesis are called assimilates. In ferns and most flowering plants the mesophyll is divided into two layers:
- An upper palisade layer of tightly packed, vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis. Its cells contain many more chloroplasts than the spongy layer. These long cylindrical cells are regularly arranged in one to five rows. Cylindrical cells, with the chloroplasts close to the walls of the cell, can take optimal advantage of light. The slight separation of the cells provides maximum absorption of carbon dioxide. This separation must be minimal to afford capillary action for water distribution. In order to adapt to their different environment (such as sun or shade), plants had to adapt this structure to obtain optimal result. Sun leaves have a multi-layered palisade layer, while shade leaves or older leaves closer to the soil, are single-layered.
- Beneath the palisade layer is the spongy layer. The cells of the spongy layer are more rounded and not so tightly packed. There are large intercellular air spaces. These cells contain less chloroplasts than those of the palisade layer. The pores or stomata of the epidermis open into substomatal chambers, connecting to air spaces between the spongy layer cells. These two different layers of the mesophyll are absent in many aquatic and marsh plants. Even an epidermis and a mesophyll may be lacking. Instead for their gaseous exchanges they use a homogenous aerenchyma (thin-walled cells separated by large gas-filled spaces). Their stomata are situated at the upper surface. Leaves are normally green in color, which comes from chlorophyll found in plastids in the chlorenchyma cells. Plants that lack chlorophyll cannot photosynthesize. Leaves in temperate, boreal, and seasonally dry zones may be seasonally deciduous (falling off or dying for the inclement season). This mechanism to shed leaves is called abscission. After the leaf is shed, a leaf scar develops on the twig. In cold autumns they sometimes turn yellow, bright orange or red as various accessory pigments (carotenoids and anthocyanins) are revealed when the tree responds to cold and reduced sunlight by curtailing chlorophyll production.

Veins

The veins are the vascular tissue of the leaf and are located in the spongy layer of the mesophyll. They are typical examples of pattern formation through ramification. The veins are made up of:
- xylem, which brings water from the stem into the leaf.
- phloem, which usually moves sap out, the latter containing the glucose produced by photosynthesis in the leaf. The xylem typically lies over the phloem. Both are embedded in a dense parenchyma tissue (= ground tissue), called pith, with usually some structural collenchyma tissue present.

Leaf morphology

External leaf characteristics (such as shape, margin, hairs, etc.) are important for identifying plant species, and botanists have developed a rich terminology for describing leaf characteristics. phloem Leaves may be classified in many different ways, and the type is usually characteristic of a species, although some species produce more than one type of leaf. The terminology associated with describing leaf morphology is presented (with illustrations) at [http://wikibooks.org/wiki/Botany:_Leaves_(forms) Wikibooks].

Basic leaf types

- Ferns have fronds.
- Conifer leaves are typically needle-, awl-, or scale-shaped
- Angiosperm (flowering plant) leaves: the standard form includes stipules, petiole, and lamina.
- Microphyll leaves.
- Sheath leaves (type found in most grasses).
- Other specialized leaves.

Arrangement on the stem

As a stem grows, leaves tend to appear arranged around the stem in away that optimizes yield of light. In essence, leaves come off the stem in a spiral pattern, either clockwise or counterclockwise, with (depending upon the species) the same angle of divergence. There is a regularity in these angles and they follow the numbers in a Fibonacci series: 1/2, 2/3, 3/5, 5/8, 8/13, 13/21, 21/34, 34/55, 55/89. This series tends to a limit of 360° x 34/89 = 137,52 or 137° 30', an angle known mathematically as the 'golden angle'. In the series, the numerator gives the number of complete turns or gyres until the leaf arrives at the initial position. The denominator gives the number of leaves in the arrangement. This can be demonstrated by the following:
- alternate leaves have an angle of 180° (or 1/2)
- 120° (or 1/3) : three leaves in one circle
- 144° (or 2/5) : five leaves in two gyres
- 135° (or 3/8) : eight leaves in three gyres. The fact that an arrangement of anything in nature can be described by a mathematical formula is not in itself mysterious. Mathematics is the science of discovering numerical relationships and applying formulae to these relationships. The formulae themselves can provide clues to the underlying physiological processes that, in this case, determine where the next leaf bud will form in the elongating stem. However, we can more easily describe the arrangement of leaves using the following terms:
- Alternate — leaf attachments singular at nodes, and leaves alternate direction, to a greater or lesser degree, along the stem.
- Opposite — leaf attachments paired at each node; decussate if, as typical, each successive pair is rotated 90° going along the stem; or distichous if not rotated, but two-ranked (in the same plane).
- Whorled — three or more leaves attach at each point or node on the stem. As with opposite leaves, successive whorls may or may not be decussate, rotated by half the angle between the leaves in the whorl (i.e., successive whorls of three rotated 60°, whorls of four rotated 45°, etc). Note: opposite leaves may appear whorled near the tip of the stem.
- Rosulate — leaves form a rosette ( = a cluster of leaves growing in crowded circles from a common center). Fibonacci series

Divisions of the lamina (blade)

Two basic forms of leaves can be described considering the way the blade is divided. A simple leaf has an undivided blade. However, the leaf shape may be one of lobes, but the gaps between lobes do not reach to the main vein. A compound leaf has a fully subdivided blade, each leaflet of the blade separated along a main or secondary vein. Because each leaflet can appear to be a "simple leaf", it is important to recognize where the petiole occurs to identify a compound leaf. Compound leaves are a characteristic of some families of higher plants, such as the Fabaceae.
- Palmately compound leaves have the leaflets radiating from the end of the petiole, like fingers off the palm of a hand. There is no rachis, e.g. Cannabis (hemp) and Aesculus (buckeyes).
- Pinnately compound leaves have the leaflets arranged along the main or mid-vein (called a rachis in this case).
- odd pinnate: with a terminal leaflet, e.g. Fraxinus (ash).
- even pinnate: lacking a terminal leaflet, e.g. Swietenia (mahogany).
- Bipinnately compound leaves are twice divided: the leaflets are arranged along a secondary vein that is one of several branching off the rachis. Each leaflet is called a pinnule. The pinnules on one secondary vein are called pinna; e.g. Albizia (silk tree).
- trifoliate: a pinnate leaf with just three leaflets, e.g. Trifolium (clover), Laburnum (laburnum).
- pinnatifid: pinnately dissected to the midrib, but with the leaflets not entirely separate, e.g. some Sorbus (whitebeams). ;Characteristics of the petiole:
- Petiolated leaves have a petiole.
- In peltate leaves, the petiole attaches to the blade inside from the blade margin.
- Sessile or clasping leaves do not have a petiole. In sessile leaves the blade attaches directly to the stem. In clasping leaves, the blade partially or wholly surrounds the stem, giving the impression that the shoot grows through the leaf such as in Claytonia perfoliata of the purslane family (Portulacaceae). In some Acacia species, such as the Koa Tree (Acacia koa), the petioles are expanded or broadened and function like leaf blades; these are called phyllodes. There may or may not be normal pinnate leaves at the tip of the phyllode. ;Characteristics of the stipule
- A stipule, present on the leaves of many dicotyledons, is an appendage on each side at the base of the petiole, resembling a small leaf. They may be lasting and not be shed (a stipulate leaf, such as in roses and beans); or be shed as the leaf expands, leaving a stipule scar on the twig (an exstipulate leaf).
- The situation, arrangement, and structure of the stipules is called the stipulation.
- free
- adnate : fused to the petiole base
- ochreate : provided with ochrea, or sheath-formed stipules, e.g. rhubarb,
- encircling the petiole base
- interpetiolar : between the petioles of two opposite leaves.
- intrapetiolar : between the petiole and the subtending stem

Venation (arrangement of the veins)

rhubarb There are two subtypes of venation, craspedodromus (the major veins stretch up to the margin of the leaf) and camptodromous (major veins come close to the margin, but bend before they get to it).
- Feather-veined, reticulate — the veins arise pinnately from a single mid-vein and subdivide into veinlets. These, in turn, form a complicated network. This type of venation is typical for dicotyledons.
- Pinnate-netted, penniribbed, penninerved, penniveined; the leaf has usually one main vein (called the mid-vein), with veinlets, smaller veins branching off laterally, usually somewhat parallel to each other; eg Malus (apples).
- Three main veins originate from the base of the lamina, as in Ceanothus.
- Palmate-netted, palmate-veined, fan-veined; several main veins diverge from near the leaf base where the petiole attaches, and radiate toward the edge of the leaf; e.g. most Acer (maples).
- Parallel-veined, parallel-ribbed, parallel-nerved, penniparallel — veins run parallel most the length of the leaf, from the base to the apex. Commissural veins (small veins) connect the major parallel veins. Typical for most monocotyledons, such as grasses.
- Dichotomous — There are no dominant bundles, with the veins forking regularly by pairs; found in Ginkgo and some pteridophytes.
pteridophyte

Leaf terminology

;Shape See Leaf shape

Margins (edge)

The leaf margin is characteristic for a genus and aids in determining the species.
- entire: even; with a smooth margin; without toothing
- ciliate: fringed with hairs
- crenate: wavy-toothed; dentate with rounded teeth, such as Fagus (beech)
- dentate: toothed, such as Castanea (chestnut)
- coarse-toothed: with large teeth
- glandular toothed: with teeth that bear glands.
- denticulate: finely toothed
- doubly toothed: each tooth bearing smaller teeth, such as Ulmus (elm)
- lobate: indented, with the indentations not reaching to the center, such as many Quercus (oaks)
- palmately lobed: indented with the indentations reaching to the center, such as Humulus (hop).
- serrate: saw-toothed with asymmetrical teeth pointing forward, such as Urtica (nettle)
- serrulate: finely serrate
- sinuate: with deep, wave-like indentations; coarsely crenate, such as many Rumex (docks)
- spiny: with stiff, sharp points, such as some Ilex (hollies) and Cirsium (thistles).

Tip of the leaf

- acuminate: long-pointed, prolonged into a narrow, tapering point in a concave manner.
- acute: ending in a sharp, but not prolonged point
- cuspidate: with a sharp, elongated, rigid tip; tipped with a cusp.
- emarginate: indented, with a shallow notch at the tip.
- mucronate: abruptly tipped with a small short point, as a continuation of the midrib; tipped with a mucro.
- mucronulate: mucronate, but with a smaller spine.
- obcordate: inversely heart-shaped, deeply notched at the top.
- obtuse: rounded or blunt
- truncate: ending abruptly with a flat end, that looks cut off.

Base of the leaf

- acuminate: coming to a sharp, narrow, prolonged point.
- acute: coming to a sharp, but not prolonged point.
- auriculate: ear-shaped
- cordate: heart-shaped with the norch away from the stem.
- cuneate: wedge-shaped.
- hastate: shaped like an halberd and with the basal lobes pointing outward.
- oblique: slanting.
- reniform: kidney-shaped but rounder and broader than long.
- rounded: curving shape.
- sagittate: shaped like an arrowhead and with the acute basal lobes pointing downward.
- truncate: ending abruptly with a flat end, that looks cut off.

Surface of the leaf

The surface of a leaf can be described by several botanical terms:
- farinose: bearing farina; mealy, covered with a waxy, whitish powder.
- glabrous: smooth, not hairy.
- glaucous: with a whitish bloom; covered with a very fine, bluish-white powder.
- glutinous: sticky, viscid.
- papillate, papillose: bearing papillae (minute, nipple-shaped protuberances).
- pubescent: covered with erect hairs (especially soft and short ones)
- punctate: marked with dots; dotted with depressions or with translucent glands or colored dots.
- rugose: deeply wrinkled; with veins clearly visible.
- scurfy: covered with tiny, broad scalelike particles.
- tuberculate: covered with tubercles; covered with warty prominences.
- verrucose: warted, with warty outgrowths.
- viscid, viscous: covered with thick, sticky secretions.

Hairiness (trichomes)

Leaves can show several degrees of hairiness. The meaning of several of the following terms can overlap. See also : Trichome.
- glabrous: no hairs of any kind present.
- arachnoid, arachnose: with many fine, entangled hairs giving a cobwebby appearance.
- barbellate: with finely barbed hairs (barbellae).
- bearded: with long, stiff hairs.
- bristly: with stiff hair-like prickles.
- canescent: hoary with dense grayish-white pubescence.
- ciliate: marginally fringed with short hairs (cilia).
- ciliolate: minutely ciliate.
- floccose: with flocks of soft, woolly hairs, which tend to rub off.
- glandular: with a gland at the tip of the hair.
- hirsute: with rather rough or stiff hairs.
- hispid: with rigid, bristly hairs.
- hispidulous: minutely hispid.
- hoary: with a fine, close grayish-white pubescence.
- lanate, lanose: with woolly hairs.
- pilose: with soft, clearly separated hairs.
- puberulent, puberulous: with fine, minute hairs.
- pubescent: with soft, short and erect hairs.
- scabrous, scabrid: rough to the touch
- sericeous: silky appearance through fine, straight and appressed (lying close and flat) hairs.
- silky: with adpressed, soft and straight pubescence.
- stellate, stelliform: with star-shaped hairs.
- strigose: with appressed, sharp, straight and stiff hairs.
- tomentose: densely pubescent with matted, soft white woolly hairs.
- cano-tomentose: between canescent and tomentose
- felted-tomentose: woolly and matted with curly hairs.
- villous: with long and soft hairs, usually curved.
- woolly: with long, soft and tortuous or matted hairs.

Adaptations

In order to survive in a harsh environment, leaves can adapt in the following ways:
- Hairs develop on the leaf surface to trap humidity in dry climates, creating a large boundary layer to lessen water loss
- Leaves rustle to move humidity away from the surface reducing the boundary layer resistance between the leaf and the air.
- Plant prickles are modified clusters of epidermal hairs
- Waxy leaf surfaces form to prevent water loss
- Small, shiny leaves to deflect the sun's rays
- Thicker leaves to store water (e.g. rhubarb)
- Change to spines instead of laminar (blade) leaves (e.g. cactus)
- Shrink (to phyllodes) or disappear (with the appearance of cladodes), as photosynthetic functions are transferred to the leaf stem (Acacia species)
- Change shape to deflect wind or reduce wind resistance
- Leaves to trap insects (e.g. pitcher plant)
- Change to bulb parts to store food (e.g. onion)
- Produce aromatic oils to deter herbivores (e.g. eucalypts)
- Protect as spines, which are modified leaves.

External links

- [http://www.ibiblio.org/botnet/glossary/b_i.html Position and Arrangement] Category:Photosynthesis Category:Plant physiology Category:plant morphology Category:Plant anatomy ko:잎 ja:葉 th:ใบไม้

Gymnosperm

]] Gymnosperms (Gymnospermae) is a name for a group of seed-bearing (and thus vascular) plants. The term gymnosperm comes from the Greek word gumnospermos, literally meaning "naked seed": this is because the seeds of these plants are not formed in an ovule that is enclosed (and developing into a fruit, in the angiosperms), but naked on the scales of a cone or cone-like structure. The production of seeds distinguishes the gymnosperms (along with the angiosperms) from other members of the vascular plants. Thus together they are called seed plants (Spermatophyta). Gymnosperms are heterosporous, producing microspores that develop into pollen grains and megaspores that are retained in an ovule. After fertilization (joining of the micro- and megaspore), the resulting embryo, along with other cells comprising the ovule, develops into a seed. The seed is a sporophyte resting stage. In early classification schemes, the gymnosperms (Gymnospermae) "naked seed" plants were regarded as a "natural" group. However, fossil finds suggest that the angiosperms evolved from a gymnosperm ancestor, which would make the gymnosperms a paraphyletic taxon. Modern cladistics only accepts taxa that are monophyletic, traceable to a common ancestor and inclusive of all descendants of that common ancestor. So, while the term gymnosperm is still widely used for non-angiosperm seed-bearing plants, the plant species once treated as gymnosperms are usually distributed among four groups, which can be given equal rank as divisions within the Kingdom Plantae. These groups are:
- Division Pinophyta – Conifers
- Division Ginkgophyta – Ginkgo
- Division Cycadophyta – Cycads
- Division Gnetophyta – Gnetum, Ephedra, Welwitschia

External links

- [http://www.biologie.uni-hamburg.de/b-online/earle/ Gymnosperm Database] sort31 Gymnospermae sort31 Gymnospermae category: gymnosperms ko:겉씨식물 ja:裸子植物

Dioecious

Plant sexuality deals with the wide variety of sexual reproduction systems found across the plant kingdom. That plants employ many different strategies to engage in sexual reproduction was used, from just a structural perspective, by Carolus Linnaeus (1735) to propose a system of classification of flowering plants, and later this subject received attention from Charles Darwin (1877). Flowers, the reproductive organs of angiosperms, are more varied than the equivalent structures of any other group of organisms, and flowering plants also have an unrivalled diversity of sexual systems (Barrett, 2002). But sexuality and the significance of sexual reproductive strategies is no less important in all of the other plant groups. The breeding system is the single most important determinant of the mating structure of nonclonal plant populations. The mating structure in turn controls the amount and distribution of genetic variation, a central element in the evolutionary process (Costich, 1995).

Terminology

The complexity of the systems and devices used by plants to achieve sexual reproduction has resulted in botanists and evolutionary biologists proposing numerous terms to describe structures and strategies. Dellaporta and Calderon-Urrea (1993) list and define a variety of terms used to describe the modes of sexuality at different levels in flowering plants. This list is reproduced here (taken from Molner, 2004), generalized to fit more than just plants that have flowers, and expanded to include other terms and better definitions. flower
- Individual sexual organ (a flower in angiosperms):
- Bisexual - Reproductive organ with both male and female equivalent parts (stamens and pistil in angiosperms; also called a perfect flower); another term widely used is hermaphrodite.
- Unisexual - Reproductive structure that is either functionally male or functionally female. In angiosperms this condition is also called imperfect.
- Individual plant:
- Hermaphrodite - A plant that has only hermaphrodite reproductive structures. In angiosperm terminology a synonym is monoclinous from the Greek "one bed".
- Monoecious - having unisexual flowers, conifer cones, or functionally equivalent structures of both sexes appearing on the same plant; from Greek for "one household".
- Dioecious - having unisexual flowers, conifer cones, or functionally equivalent structures occurring on different individuals; from Greek for "two households".
- Because many dioecious conifers show a tendency towards monoecy (that is, a female plant may sometimes produce small numbers of male cones or vice versa), these species are termed subdioecious (McCormick & Andresen, 1963).
- In angiosperm terminology, diclinous ("two beds") includes all species with unisexual flowers, although particularly those with only unisexual flowers, i.e. the monoecious and dioecious species.
- Gynoecious - has only female reproductive structures; the "female" plant.
- Androecious - has only male reproductive structures; the "male" plant.
- Gynomonoecious - has both hermaphrodite and female structures.
- Andromonoecious - has both hermaphrodite and male structures.
- Trimonoecious (polygamous) - male, female, and hermaphrodite structures all appear on the same plant. conifers with pollen and reduced, sterile stigma; (below) shoot with flowers from female plant; (lower right) female flower enlarged, showing stigma
and reduced, sterile stamens with no pollen]]
- Plant population
- Hermaphrodite - only hermaphrodite plants.
- Monoecious - only monoecious plants.
- Dioecious - only dioecious plants.
- Gynodioecious - both female and hermaphrodite plants present.
- Androdioecious - both male and hermaphrodite plants present.
- Trioecious (or subdioecious) - male, female, and hermaphrodite plants are all in the same population.

Morphological mechanisms

Flower morphology

A species, such as the ash (Fraxinus excelsior L.), demonstrates the possible range of variation in morphology and functionality exhibited by flowers with respect to gender. Flowers of the ash are wind-pollinated and lack petals and sepals. Structurally, the flowers may be either male, female, or hermaphrodite, the latter consisting of two anthers and an ovary ('c' below). A male flower can be morphologically male ('a' below) or a hermaphrodite flower with anthers and a rudimentary gynoecium ('b' below; functionally 'male'). Ash flowers can also be morphologically female ('e' below) or hermaphrodite and functionally female ('d' below; with vestigial anthers). 140px 150px 170px 80px 80px (Illustration from Binggeli and Power, 1999)

Physiological mechanisms

- See also: Self-incompatibility in plants, Dichogamy

Evolution

Angiosperms

It is thought that flowering plants evolved from a common hermaphrodite ancestor, and that dioecy evolved from hermaphroditism. Hermaphroditism is very common in flowering plants—about 70% are hermaphroditic, while only about 5% are dioecious and 7% are monoecious. About 7% of species exhibit gynodioecy or androdioecy, while 10% contain both unisexual and bisexual flowers (Molner, 2004). A fair degree of correlation (though far from complete) exists between dioecy/sub-dioecy and plants that have seeds dispersed by birds (both nuts and berries). It is hypothesized that the concentration of fruit in half of the plants increases dispersal efficiency; female plants can produce a higher density of fruit as they do not expend resources on pollen production, and the dispersal agents (birds) need not waste time looking for fruit on male plants.

Cultivation of dioecious plants

Cannabis is famous for being dioecious, with only the female plant desirable for psychotropic effects. It is an interesting plant from a cultivational perspective because while the males are generally separated to prevent pollination of the female plants (undesirable for various reasons), the pheromones produced by the males cause the females to produce more tetrahydrocannabinol, making their unfertilized buds more potent. Experienced growers therefore learn to keep males near enough to the females to have this effect, but far enough that fertilization is unlikely. (Though obviously some females are allowed to be fertilized in order obtain seeds with which to re-populate the crop.)

External link

- [http://waynesword.palomar.edu/ww0404.htm Plant sexuality and political correctness], vol. 4(4) (Winter 1996) at Wayne's Word.

References

- Barrett, S.C.H. 2002. The evolution of plant sexual diversity. Nature Reviews Genetics 3(4): 274-284.
- Binggeli, P. and J. Power. 1999. [http://members.lycos.co.uk/WoodyPlantEcology/species/ash.htm Gender variation in ash (Fraxinus excelsior L.)]
- Costich, D. E. 1995. Gender specialization across a climatic gradient: experimental comparison of monoecious and dioecious Ecballium. Ecology, June 1995.
- Darwin, C. 1877. The Different Forms of Flowers on Plants of the Same Species.
- Dellaporta, S.L. and A. Calderon-Urrea. 1993. Sex determination in flowering plants. The Plant Cell, 5: 1241-1251
- Linnaeus, C. 1735. Systema Naturae.
- McCormick, J. & J. W. Andresen. 1963. A subdioecious population of Pinus cembroides in southeast Arizona. Ohio J. Science, 63: 159-163.
- Molnar, Sebastian. 2004. [http://www.geocities.com/we_evolve/Plants/breeding_sys.html Plant Reproductive Systems], internet version posted February 17, 2004. Category:Botany Category:Sexuality

Arecaceae

Many; see list of Arecaceae genera Arecaceae (also known as Palmae), the Palm Family, is a family of flowering plants, belonging to the monocot order, Arecales. There are 202 currently known genera with around 2,600 species, most of which are restricted to tropical or subtropical climates. Of all the families of plants, the Arecaceae is the most easily recognizable as distinct by most persons. The type member of this family is the areca palm, the fruit of which is chewed with the betel leaf and often confused with it. The Date Palm, Rattan, and Coconut also belong to this family. Palm oil is an edible vegetable oil produced by the oil palms in the genus Elaeis. Several species are harvested for heart of palm. Palm sap is sometimes fermented to produce palm wine. The Palm Sunday festival uses palms, hence the name. Palms first appear in the fossil record around 70-80 million years ago, during the Cretaceous Period, making them one of the older families of flowering plants. Economically important genera include:
- Areca
- Arenga
- Attalea
- Bactris
- Borassus (Palmyra Palm)
- Calamus - rattan palm
- Cocos - coconut
- Copernicia - carnauba wax palm
- Elaeis - oil palm
- Euterpe Cabbage Heart Palm, and Açaí Palm
- Jessenia
- Jubaea Chilean Wine Palm and Coquito Palm
- Orbignya
- Phoenix - date palms
- Rhapis
- Roystonea - royal palm
- Sabal - palmetto
- Salacca - salak
- Trachycarpus
- Veitchia
- Wallichia
- Washingtonia See list of Arecaceae genera for a complete listing. list of Arecaceae genera list of Arecaceae genera Few palms tolerate severe cold, and the majority of the species are tropical or subtropical. The most cold-tolerant are Trachycarpus, native to eastern Asia, and Rhapidophyllum, native to the southeastern United States. For more details, see hardy palms. In the United States, different types of palm trees can be seen in tropical and mediterranean climate areas, such as Florida, (southern) California and Hawaii and along the Gulf Coast through southern Georgia, Mississippi, Alabama, and Louisiana to Texas. The southeastern state of South Carolina is nicknamed the Palmetto State because of the number of palms that line the state's Atlantic coast. Some palms can be grown as far north as Maryland, Arkansas, and even up along the Pacific coast to Oregon and Washington. There have even been known species of transplanted palms that have survived as far north as southern New Jersey [http://www.bg-map.com/palms/woodbury.html]. The desert areas of Nevada, Arizona, Utah and New Mexico are also home to some native palms. Southern Europe has two native palms, Chamaerops humilis (widespread, but mainly seen in Portugal, Spain, France, Italy and Malta) and Phoenix theophrastii (Crete; also southern Turkey). Many other palms are widely planted, with the Japanese Trachycarpus wagnerianus being grown successfully as far north as Iceland.

References

- C. H. Schultz-Schultzenstein (1832). Natürliches System des Pflanzenreichs..., 317. Berlin, Germany.
- N. W. Uhl, J. Dransfield (1987). Genera palmarum: a classification of palms based on the work of Harold E. Moore, Jr. (Allen Press, Lawrence, Kansas)

External links

- [http://www.kew.org/cgi-bin/web.dbs/genlist.pl?PALMAE Kew Botanic Garden's Palm Genera list] A list of the currently acknowledged genera by Kew Royal Botanic Gardens in London, England.
- [http://www.plantapalm.com/vpe/taxonomy/vpe_taxonomy3.htm Taxonomy of the family Arecaceae]
- [http://www.pacsoa.org.au/palms/ PACSOA] Palm and Cycad Societies of Australia palm species listing with images.
- [http://www.plantapalm.com/vpe/photos/vpe_photos.htm Plant a Palm] A website with a large amount of information on palms, their cultivation and uses. This link goes to the photo gallery via species listing. Category:Plant families Category:Palms ja:ヤシ (植物) th:ปาล์ม

Fern

Marattiopsida
Osmundopsida
Gleicheniopsida
Pteridopsida A fern, or pteridophyte, is any one of a group of some twenty thousand species of plants classified in the Division Pteridophyta, formerly known as Filicophyta. A fern is a vascular plant that differs from the more primitive lycophytes in having true leaves (megaphylls) and from the more advanced seed plants (gymnosperms and angiosperms) in lacking seeds. Like all vascular plants, it has a life cycle, often referred to as alternation of generations, characterized by a diploid sporophytic and a haploid gametophytic phase. Unlike the gymnosperms and angiosperms, in ferns the gametophyte is a free-living organism. The life cycle of a typical fern is as follows: # A sporophyte (diploid) phase produces haploid spores by meiosis; # A spore grows by cell division into a gametophyte, which typically consists of a photosynthetic prothallus # The gametophyte produces gametes (often both sperm and eggs on the same prothallus) by mitosis # A mobile, flagellate sperm fertilizes an egg that remains attached to the prothallus # The fertilized egg is now a diploid zygote and grows by mitosis into a sporophyte (the typical "fern" plant).

Fern structure

zygote Like the sporophytes of seed plants, those of ferns consist of:
- Stems: Most often an underground creeping rhizome, but sometimes an above-ground creeping stolon (e.g., Polypodiaceae), or an above-ground erect semi-woody trunk (e.g., Cyatheaceae) reaching up to 20 m in a few species (e.g., Cyathea brownii on Norfolk Island and Cyathea medullaris in New Zealand).
- Leaf: The green, photosynthetic part of the plant. In ferns, it is often referred to as a frond, but this is because of the historical division between people who study ferns and people who study seed plants, rather than because of differences in structure. New leaves typically expand by the unrolling of a tight spiral (the fiddlehead), called circinate vernation. Leaves are further divided into two types:
- Trophophyll: A leaf that does not produce spores, instead only producing sugars by photosynthesis. Analogous to the typical green leaves of seed plants.
- Sporophyll: A leaf that produces spores. These leaves are analogous to the scales of pine cones or to stamens and pistil in gymnosperms and angiosperms, respectively. Unlike the seed plants, however, the sporophylls of ferns are typically not very specialized, looking similar to trophophylls and producing sugars by photosynthesis as the trophophylls do.
- Roots: The underground non-photosynthetic structures that take up water and nutrients from soil. They are always fibrous and are structurally very similar to the roots of seed plants. The gametophytes of ferns, however, are very different from those of seed plants. They typically consist of:
- Prothallus: A green, photosynthetic structure that is one cell thick, usually heart- or kidney-shaped, 3-10 mm long and 2-8 mm broad. The thallus produces gametes by means of:
- Antheridia: Small spherical structures that produce flagellate sperm.
- Archegonia: A flask-shaped structure that produces a single egg at the bottom, reached by the sperm by swimming down the neck.
- Rhizoids: root-like structures that consist of single greatly-elongated cells that take up water and nutrients.

Evolution and classification

Ferns first appear in the fossil record in the early-Carboniferous epoch. By the Triassic, the first evidence of ferns related to several modern families appeared. The "great fern radiation" occurred in the late-Cretaceous, when many modern families of ferns first appeared. Ferns have traditionally been grouped in the Class Filices, but modern classifications assign them their own division in the plant kingdom, called Pteridophyta. Two related groups of plants, commonly known as ferns, are actually more distantly related to the main group of "true" ferns. These are the whisk ferns (Psilophyta) and the adders-tongues, moonworts, and grape-ferns (Ophioglossophyta). The Ophioglossophytes were formerly considered true ferns and grouped in the Family Ophioglossaceae, but were subsequently found to be more distantly related. Some classification systems include the Psilopytes and Ophioglossophytes in Division Pteridophyta, while others assign them to separate divisions. Modern phylogeny indicates that the Ophioglossophytes, Psilopytes, and true ferns together constitute a monophyletic group, descended from a common ancestor. The true ferns may be subdivided into four main groups, or classes (or orders if the true ferns are considered as a class):
- Marattiopsida
- Osmundopsida
- Gleicheniopsida
- Pteridopsida The last group includes most plants familiarly known as ferns. The Marattiopsida are a primitive group of tropical ferns with a large, fleshy rhizome, and are now thought to be a sibling taxon to the main group of ferns, the leptosporangiate ferns, which include the other three groups listed above. Modern research indicates that the Osmundopsida diverged first from the common ancestor of the leptosporangiate ferns, followed by the Gleichenopsida. Pteridopsida Pteridopsida Pteridopsida Pteridopsida A more complete classification scheme follows:
- Division: Pteridophyta
- Class: Marattiopsida
- Order: Marattiales
- Order: Christenseniales
- Class: Osmundopsida
- Order: Osmundales (the flowering ferns)
- Class: Gleicheniopsida
- Subclass: Gleicheniatae
- Order: Gleicheniales (the forked ferns)
- Order: Dipteridales
- Order: Matoniales
- Subclass: Hymenophyllatae
- Order: Hymenophyllales (the filmy ferns)
- Subclass: Hymenophyllopsitae
- Order: Hymenophyllopsidales
- Class: Pteridopsida
- Subclass: Schizaeatae
- Order: Schizeales (including the climbing ferns)
- [heterosporous ferns]
- Order: Marsileales (Hydropteridales) (the water-clovers, mosquito fern, water-spangle)
- Subclass: Cyatheatae
- Order: Cyatheales (the tree ferns)
- Order: Plagiogyriales
- Order: Loxomales
- Subclass: Pteriditae
- Order: Lindseales
- Order: Pteridales (including the brakes and maidenhair ferns)
- Order: Dennstaedtiales (the cup ferns, including bracken)
- Subclass: Polypoditae
- Order: Aspleniales (the spleenworts)
- Order: Athyriales (including the lady ferns, ostrich fern, maiden ferns, etc.)
- Order: Dryopteridales (the wood ferns and sword ferns)
- Order: Davalliales (including the rabbits-foot ferns and Boston ferns)
- Order: Polypodiales (including the rock-cap ferns or Polypodies)

Economic uses

Ferns are not of major economic importance, with one possible exception. Ferns of the genus Azolla, which are very small, floating plants that do not look like ferns, called mosquito fern, are used as a biological fertilizer in the rice paddies of southeast Asia, taking advantage of their ability to fix nitrogen from the air into compounds that can then be used by other plants. Other ferns with some economic significance include:
- Dryopteris filix-mas (male fern), used as a vermifuge
- Rumohra adiantoides (floral fern), extensively used in the florist trade
- Osmunda regalis (royal fern) and Osmunda cinnamomea (cinnamon fern), the root fiber being used horticulturally; the fiddleheads of O. cinnamomea are also used as a cooked vegetable
- Matteuccia struthiopteris (ostrich fern), the fiddleheads used as a cooked vegetable in North America
- Pteridium aquilinum (bracken), the fiddleheads used as a cooked vegetable in Japan
- Diplazium esculentum (vegetable fern), a source of food for some native societies
- Tree ferns, used as building material in some tropical locales In addition, a great many ferns are grown in horticulture.

Misunderstood names

Several non-fern plants are called "ferns" and are sometimes popularly believed to be ferns in error. These include:
- "Asparagus fern" - This may apply to one of several species of the monocot genus Asparagus, which are flowering plants. A better name would be "fern asparagus".
- "Sweetfern" - This is a shrub of the genus Comptonia.
- "Air fern" - This is an unrelated aquatic animal that is related to a coral; it is harvested, dried, dyed green, then sold as plant that can "live on air". It looks like a fern but is actually a skeleton. In addition, the book Where the Red Fern Grows has elicited many questions about the mythical "red fern" named in the book. There is no such known plant, although there has been speculation that the Oblique grape-fern, Sceptridium dissectum, could be referred to here, because it is known to appear on disturbed sites and its fronds may redden over the winter.

External links and sources

- Moran, Robbin C. (2004). A Natural History of Ferns. Portland, OR: Timber Press. ISBN 0-88192-667-1.
- [http://tolweb.org/tree?group=Filicopsida&contgroup=Embryophytes Tree of Life Web Project: Filicopsida]
- A classification of the [http://www.anbg.gov.au/projects/fern/taxa/classification.html ferns and their allies]
- [http://www.jaknouse.athens.oh.us/ferns/bookfern.html A fern book bibliography]
- [http://www1.akira.ne.jp/~unzen/pteridophyta.html Register of fossil Pteridophyta]
- [http://delta-intkey.com/britfe/ L. Watson and M.J. Dallwitz (2004 onwards). The Ferns (Filicopsida) of the British Isles.] http://delta-intkey.com Category:Pteridophyta ja:シダ植物門

Division (biology)

:This article discusses categorisations of organisms. For a different meaning in biology, see cell division. In biology, the equivalent of a phylum in the plant or fungi kingdom is called a division. The main plant divisions, in the order in which they probably evolved, are the mosses (Division Bryophyta), the ferns (Division Filicophyta), the horsetails (Division Sphenophyta), the Cycads (Division Cycadophyta), the Ginkgo (Division Ginkgophyta), the conifers (Division Pinophyta), the Gnetophytes (Division Gnetophyta), and the angiosperms (Division Anthophyta). Angiosperms are the flowering plants that now dominate the plant world (80% of all vascular plants are angiosperms). rank02a th:ส่วน (ชีววิทยา)

South America

South America is a continent, with most of its area in the Southern Hemisphere. South America is situated between the Pacific Ocean and the Atlantic Ocean. Commonly referred to as part of America, like North America, South America is named after Amerigo Vespucci, who was the first European to suggest that the Americas were not the East Indies, but a previously undiscovered New World. South America has an area of 17,821,601 km² (6,880,959 sq mi), or almost 3.5% of the Earth's surface. As of 2005, its population was estimated at more than 371,200,000. South America ranks fourth in area (after Asia, Africa, and North America) and fifth in population (after Asia, Africa, Europe, and North America).Europe __TOC__

Geography

The classification of its geographic location is subject to dispute, as in some non-English speaking regions of the world, the Americas are a continent and North, Central and South America are its subcontinents. In English-speaking and certain other regions of the world, North and South America are considered to be continents and their union is referred to as the supercontinent of the Americas. The classification given to South America, as a subcontinent in a continent or a continent in a supercontinent, depends entirely on regional preferences. It became attached to North America only recently (geologically speaking) with the formation of the Isthmus of Panama some 3 million years ago, which resulted in the Great American Interchange. The Andes, likewise a comparatively young and seismically restless mountain range, run down the western edge of the continent; the land to the east of the Andes is largely tropical rain forest, the vast Amazon River basin. The continent also contains drier regions such as Patagonia and the extremely arid Atacama desert. The region of South America also includes various islands, most of which belong to countries on the continent. The Caribbean territories are grouped with North America. The South American nations that border the Caribbean Sea – including Colombia, Venezuela, Guyana, Suriname, and French Guiana – are also known as Caribbean South America. Major natural resources are copper, iron ore, tin and oil. The many resources in South America have become useful around the world, but they have failed to diversify their economies. This has lead to major highs and lows in their economy causing instability. South America is home to many interesting species of animals including parrots, tarantulas, snakes, and mammals. The largest country in South America by far, in both area and population, is Brazil followed by Argentina. Regions in South America include the Andean States, the Guianas, the Southern Cone, and Eastern South America.

History

South America is thought to have been first inhabited by people crossing the Bering Land Bridge, now the Bering strait, though there are also suggestions of migration from the southern Pacific Ocean.

Chavín

The Chavín established a trade network and developed agriculture by 900 BC, according to some estimates and archeological finds. Artifacts were found at a site called Chavín de Huantar in modern Peru at an elevation of 3,177 meters. Chavín civilization spanned 900 BC to 300 BC.

Inca

Holding their capital at the great city of