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The gymnosperms (/ ˈ dʒ ɪ m n ə ˌ s p ɜːr m z,-n oʊ-/ ⓘ nə-spurmz, -noh-; lit. ' revealed seeds ') are a group of woody, perennial seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include conifers, cycads, Ginkgo, and gnetophytes, forming the clade Gymnospermae [2] The term gymnosperm comes from the ...
The Lyginopteridales are an extinct group of seed plants known from the Paleozoic.They were the first plant fossils to be described as pteridosperms (a polyphyletic group sometimes referred to as "seed ferns") and, thus, the group on which the concept of pteridosperms was first developed; [2] they are the stratigraphically oldest-known pteridosperms, occurring first in late Devonian strata; [3 ...
Gnetophyta (/ n ɛ ˈ t ɒ f ɪ t ə, ˈ n ɛ t oʊ f aɪ t ə /) is a division of plants (alternatively considered the subclass Gnetidae or order Gnetales), grouped within the gymnosperms (which also includes conifers, cycads, and ginkgos), that consists of some 70 species across the three relict genera: Gnetum (family Gnetaceae), Welwitschia (family Welwitschiaceae), and Ephedra (family ...
Some authors have suggested due to similarities between their seed coats, Bennettitales form a clade with the gymnosperm orders of Gnetales and Erdtmanithecales, dubbed the "BEG group". [23] However, this proposal has been contested by other authors, who contend that these similarities are only superficial and do not indicate a close ...
In both gymnosperms and angiosperms, the young plant contained in the seed, begins as a developing egg-cell formed after fertilization (sometimes without fertilization in a process called apomixis) and becomes a plant embryo. This embryonic condition also occurs in the buds that form on stems. The buds have tissue that has differentiated but ...
A simplified diagram of a bordered pit-pair with a torus and margo. The top shows an unobstructed pit and the bottom shows an aspirated pit, with the margo flexing under stress. The torus and margo are characteristic features of bordered pit-pairs in gymnosperms, such as Coniferales, Ginkgo, and Gnetales. In other vascular plants, the torus is ...
In gymnosperms and most flowering plants, only one of the four megaspores is functional at maturity, and the other three soon degenerate. The megaspore that remains divides mitotically and develops into the gametophyte, which eventually produces one egg cell . [ 2 ]
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