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Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these, the microspore , is male and the larger megaspore is female. Heterospory evolved during the Devonian period from isospory independently in several plant groups: the clubmosses , the ferns including the arborescent ...
There is debate as to whether endospory or heterospory evolved first. Some debate centers upon the requirement of endospory to develop before heterospory. [2] Endospory is assumed to follow heterospory but it has been suggested that without endospory, early plant species dependency on water fertilization and environmental impacts on gametophytic gene expression would have reduced the chances ...
Marsileaceae (/ m ɑːr ˌ s ɪ l i ˈ eɪ s i. iː /) is a small family of heterosporous aquatic and semi-aquatic ferns, though at first sight they do not physically resemble other ferns.
During the Devonian period several plant groups independently evolved heterospory and subsequently the habit of endospory, in which the gametophytes develop in miniaturized form inside the spore wall. By contrast in exosporous plants, including modern ferns, the gametophytes break the spore wall open on germination and develop outside it.
Plant ovules with megasporocytes before meiosis: Gymnosperm ovule on left, angiosperm ovule (inside ovary) on right. After megasporogenesis, the megaspore develops into the female gametophyte (the embryo sac) in a process called megagametogenesis.
The seed plant gametophyte life cycle is even more reduced than in basal taxa (ferns and lycophytes). Seed plant gametophytes are not independent organisms and depend upon the dominant sporophyte tissue for nutrients and water. With the exception of mature pollen, if the gametophyte tissue is separated from the sporophyte tissue it will not ...
Cycads produce strobili, both pollen-producing and seed-producing, that are composed of sporophylls. Ginkgo produces microsporophylls aggregated into a pollen strobilus. Ovules are not born on sporophylls [citation needed]. Gymnosperms, like Ginkgo and cycads, produce microsporophylls, aggregated into pollen strobili. However, unlike these ...
Pteris platyzomopsis has been known by the synonym Platyzoma microphyllum. [1] The genus Platyzoma has been placed as the only species in family Platyzomataceae. [4] [2] Tryon has speculated that the species, with its incipient heterospory, unusual chromosome number (2n=78) and other features, may represent a stage transitional to the heterosporous aquatic ferns.