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The gymnosperms are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and Gnetales. The term "gymnosperm" comes from the Greek composite word ''γυμνόσπερμος'' (γυμνός gymnos, "naked" and σπέρμα sperma, "seed"), meaning "naked seeds", after the unenclosed condition of their seeds (called ovules in their unfertilized state). Their naked condition stands in contrast to the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, often modified to form cones, or at the end of short stalks as in ''Ginkgo''. The gymnosperms and angiosperms together compose the spermatophytes or seed plants. By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes (''Gnetum'', ''Ephedra'' and ''Welwitschia''), and ''Ginkgo'' (a single living species). ==Classification== In early classification schemes, the gymnosperms (Gymnospermae) were regarded as a "natural" group. There is conflicting evidence on the question of whether the living gymnosperms form a clade.〔(【引用サイトリンク】 Angiosperm Phylogeny Website - Seed Plant Evolution )〕 The fossil record of gymnosperms includes many distinctive taxa that do not belong to the four modern groups, including seed-bearing trees that have a somewhat fern-like vegetative morphology (the so-called "seed ferns" or pteridosperms.)〔Hilton, Jason, and Richard M. Bateman. 2006. Pteridosperms are the backbone of seed-plant phylogeny. ''Journal of the Torrey Botanical Society'' 133: 119-168 ((abstract ))〕 When fossil gymnosperms such as Bennettitales, ''Caytonia'' and the glossopterids are considered, it is clear that angiosperms are nested within a larger gymnosperm clade, although which group of gymnosperms is their closest relative remains unclear. For the most recent classification on extant gymnosperms see Christenhusz ''et al.'' (2011).〔Christenhusz, M.J.M., J.L. Reveal, A. Farjon, M.F. Gardner, R.R. Mill, and M.W. Chase (2011). A new classification and linear sequence of extant gymnosperms. ''Phytotaxa'' 19:55-70. http://www.mapress.com/phytotaxa/content/2011/f/pt00019p070.pdf〕 Subclass Cycadidae *Order Cycadales * *Family Cycadaceae: ''Cycas'' * *Family Zamiaceae: ''Dioon'', ''Bowenia'', ''Macrozamia'', ''Lepidozamia'', ''Encephalartos'', ''Stangeria'', ''Ceratozamia'', ''Microcycas'', ''Zamia''. Subclass Ginkgoidae *Order Ginkgoales * *Family Ginkgoaceae: ''Ginkgo'' Subclass Gnetidae *Order Welwitschiales * *Family Welwitschiaceae: ''Welwitschia'' *Order Gnetales * *Family Gnetaceae: ''Gnetum'' *Order Ephedrales * *Family Ephedraceae: ''Ephedra'' Subclass Pinidae *Order Pinales * *Family Pinaceae: ''Cedrus'', ''Pinus'', ''Cathaya'', ''Picea'', ''Pseudotsuga'', ''Larix'', ''Pseudolarix'', ''Tsuga'', ''Nothotsuga'', ''Keteleeria'', ''Abies'' *Order Araucariales * *Family Araucariaceae: ''Araucaria'', ''Wollemia'', ''Agathis'' * *Family Podocarpaceae: ''Phyllocladus'', ''Lepidothamnus'', ''Prumnopitys'', ''Sundacarpus'', ''Halocarpus'', ''Parasitaxus'', ''Lagarostrobos'', ''Manoao'', ''Saxegothaea'', ''Microcachrys'', ''Pherosphaera'', ''Acmopyle'', ''Dacrycarpus'', ''Dacrydium'', ''Falcatifolium'', ''Retrophyllum'', ''Nageia'', ''Afrocarpus'', ''Podocarpus'' *Order Cupressales * *Family Sciadopityaceae: ''Sciadopitys'' * *Family Cupressaceae: ''Cunninghamia'', ''Taiwania'', ''Athrotaxis'', ''Metasequoia'', ''Sequoia'', ''Sequoiadendron'', ''Cryptomeria'', ''Glyptostrobus'', ''Taxodium'', ''Papuacedrus'', ''Austrocedrus'', ''Libocedrus'', ''Pilgerodendron'', ''Widdringtonia'', ''Diselma'', ''Fitzroya'', ''Callitris'' (incl. ''Actinostrobus''), ''Neocallitropsis'', ''Thujopsis'', ''Thuja'', ''Fokienia'', ''Chamaecyparis'', ''Callitropsis'', ''Cupressus'', ''Juniperus'', ''Xanthocyparis'', ''Calocedrus'', ''Tetraclinis'', ''Platycladus'', ''Microbiota'' * *Family Taxaceae: ''Austrotaxus'', ''Pseudotaxus'', ''Taxus'', ''Cephalotaxus'', ''Amentotaxus'', ''Torreya'' 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「gymnosperm」の詳細全文を読む スポンサード リンク
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