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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, and Ginkgo. [2] The life cycle of a gymnosperm involves alternation of generations, with a dominant diploid sporophyte phase, and a reduced haploid gametophyte phase, which is dependent on the ...
Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (/ p ɪ ˈ n ɒ f ɪ t ə, ˈ p aɪ n oʊ f aɪ t ə /), also known as Coniferophyta (/ ˌ k ɒ n ɪ f ə ˈ r ɒ f ɪ t ə,-oʊ f aɪ t ə /) or Coniferae. The division contains a single extant class, Pinopsida.
The name comes from the Greek for "naked seed"; the egg cells are not protected by ovaries, as in flowering plants. [4] Gymnosperms are divided into 12 families of trees, shrubs and woody vines. [5] Sequoiadendron giganteum, the giant redwood, is the largest tree in the world, and Sequoia sempervirens, the coastal redwood, is the tallest. [6]
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 ...
A mature female big-cone pine (Pinus coulteri) cone, the heaviest pine cone A young female or seed cone on a Norway spruce (Picea abies) Immature male or pollen cones of Swiss pine (Pinus cembra) A conifer cone or, in formal botanical usage, a strobilus, pl.: strobili, is a seed-bearing organ on gymnosperm plants, especially in conifers and cycads.
However, molecular studies (and some more recent morphological [7] [8] and fossil [9] papers) have generally shown a clade of gymnosperms, with the gnetophytes in or near the conifers. For example, one common proposed set of relationships is known as the gne-pine hypothesis and looks like: [ 10 ] [ 11 ] [ 12 ]
The seeds of conifers, the largest group of gymnosperms, are enclosed in a cone and most species have seeds that are light and papery that can be blown considerable distances once free from the cone. [91] Sometimes the seed remains in the cone for years waiting for a trigger event to liberate it.
Among the seed plants, the gymnosperms are a sister group to the subclass Magnoliidae (angiosperms or flowering plants). There are about 1000 extant gymnosperm species, distributed over about 12 families and 83 genera. Many of these genera are monotypic (41%), and another 27% are oligotypic (2–5 species). [27]