Today gymnosperms are the most threatened of all plant groups. The other extant groups are the 95–100 species of Gnetales and one species of Ginkgo. A majority of cycads are native to tropical climates and are most abundantly found in regions near the equator. Agathis in Araucariaceae and Nageia in Podocarpaceae have broad, flat strap-shaped leaves.Ĭycads are the next most abundant group of gymnosperms, with two or three families, 11 genera, and approximately 338 species. The leaves of many conifers are long, thin and needle-like, while other species, including most Cupressaceae and some Podocarpaceae, have flat, triangular scale-like leaves. Ĭonifers are by far the most abundant extant group of gymnosperms with six to eight families, with a total of 65–70 genera and 600–630 species (696 accepted names). There are no herbaceous gymnosperms and compared to angiosperms they occupy fewer ecological niches, but have evolved both parasites ( Parasitaxus), epiphytes ( Zamia pseudoparasitica) and rheophytes ( Retrophyllum minus). The soft and highly parenchymatous wood in cycads is poorly lignified, and their main structural support comes from an armor of sclerenchymatous leaf bases covering the stem, with the exception of species with underground stems. Zamia integrifolia, a cycad native to FloridaĪll gymnosperms are perennial woody plants, apart from the cycads. Evidence has also been found that mid-Mesozoic gymnosperms were pollinated by Kalligrammatid lacewings, a now-extinct family with members which (in an example of convergent evolution) resembled the modern butterflies that arose far later. The scorpionflies likely engaged in pollination mutualisms with gymnosperms, long before the similar and independent coevolution of nectar-feeding insects on angiosperms. It has been suggested that during the mid-Mesozoic era, pollination of some extinct groups of gymnosperms was by extinct species of scorpionflies that had specialized proboscis for feeding on pollination drops. Early characteristics of seed plants are evident in fossil progymnosperms of the late Devonian period around 383 million years ago. The radiation of gymnosperms during the late Carboniferous appears to have resulted from a whole genome duplication event around 319 million years ago. It was previously widely accepted that the gymnosperms originated in the Late Carboniferous period, replacing the lycopsid rainforests of the tropical region, but more recent phylogenetic evidence indicates that they diverged from the ancestors of angiosperms during the Early Carboniferous. Over 1000 living species of gymnosperm exist. Some genera have mycorrhiza, fungal associations with roots ( Pinus), while in some others ( Cycas) small specialised roots called coralloid roots are associated with nitrogen-fixing cyanobacteria.ĭiversity and origin Encephalartos sclavoi cone, about 30 cm long About 65% of gymnosperms are dioecious, but conifers are almost all monoecious. īy far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes ( Gnetum, Ephedra and Welwitschia), and Ginkgo biloba (a single living species). Newer classification place the gnetophytes among the conifers. The gymnosperms are subdivided into five Divisions, four of which, the Cycadophyta, Ginkgophyta, Gnetophyta, and Pinophyta (also known as Coniferophyta) are still in existence while the Pteridospermatophyta are now extinct. The gymnosperms and angiosperms together comprise the spermatophytes or seed plants. In that case, to specify the modern monophyletic group of gymnosperms, the term Acrogymnospermae is sometimes used. The term "gymnosperm" is often used in paleobotany to refer to (the paraphyletic group of) all non-angiosperm seed plants. They have a dominant diploid sporophyte phase and a reduced haploid gametophyte phase which is dependent on the sporophytic phase. Gymnosperm lifecycles involve alternation of generations. Gymnosperm seeds develop either on the surface of scales or leaves, which are often modified to form cones, or on their own as in yew, Torreya, Ginkgo. The non-encased condition of their seeds contrasts with the seeds and ovules of flowering plants ( angiosperms), which are enclosed within an ovary. The name is based on the unenclosed condition of their seeds (called ovules in their unfertilized state). The term gymnosperm comes from the composite word in Greek: γυμνόσπερμος ( γυμνός, gymnos, 'naked' and σπέρμα, sperma, 'seed'), literally meaning 'naked seeds'. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, Ginkgo, and gnetophytes, forming the clade Gymnospermae. The gymnosperms ( / ˈ dʒ ɪ m n ə s p ə r m z, - n oʊ-/ JIM-nə-spərmz, -noh- pronunciation i lit.
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