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Cycads / ˈ s aɪ k æ d z / are seed plants that typically have a stout and woody trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or female. Cycads vary in size from having trunks only a few centimeters to several meters tall.
The spermatophytes were traditionally divided into angiosperms, or flowering plants, and gymnosperms, which includes the gnetophytes, cycads, [5] ginkgo, and conifers. Older morphological studies believed in a close relationship between the gnetophytes and the angiosperms, [ 6 ] in particular based on vessel elements .
The extreme reduction in the size of the gametophyte and its retention within the sporophyte means that when applied to seed plants the term 'alternation of generations' is somewhat misleading: "[s]porophyte and gametophyte effectively function as a single organism". [8] Some authors have preferred the term 'alternation of phases'. [9]
Spermatophytes: Division: † Pteridospermatophyta: Groups included †Calamopityales †Callistophytales †Caytoniales †Gigantopteridales †Glossopteridales †Lyginopteridales †Medullosales †Peltaspermales †Corystospermales (also referred to as Umkomasiales) †Petriellales; Excluded Angiospermae (flowering plants) Cycadales (cycads ...
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 ...
In ferns and seed plants (including cycads, conifers, flowering plants, etc.) the sporophyte is the dominant generation; the obvious visible plant, whether a small herb or a large tree, is the sporophyte, and the gametophyte is very small. In bryophytes and ferns, the gametophytes are independent, free-living plants, while in seed plants, each ...
The sperm of members from the genus are large, as is typical of cycads, and Z. roezlii is an example; its sperm are approximately 0.4 mm long and can be seen by the unaided eye. [11] It was long believed that Zamia plants, like all cycads, relied completely on wind pollination.
A single sperm cell from Zamia roezlii is about 0.4 mm in length and is visible to the unaided eye, being the world's largest plant sperm cell. Drosophila bifurca, a species of fruit fly, has sperm that are 5.8 cm long, albeit mostly coiled tail. [3]