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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 ...
Alternation of generations is defined as the alternation of multicellular diploid and haploid forms in the organism's life cycle, regardless of whether these forms are free-living. [6] In some species, such as the alga Ulva lactuca , the diploid and haploid forms are indeed both free-living independent organisms, essentially identical in ...
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.
A segment of a jointed stem or of a fruit with constrictions between the seeds; an organ part that separates easily from the rest of the organ at a joint or articulation. articulate Jointed; separating freely, leaving a clean scar; e.g. the frond s of certain ferns where they join the rhizome. ascending 1.
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 ...
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Lycopodiopsida is a class of vascular plants also known as lycopsids, [1] lycopods, or lycophytes. Members of the class are also called clubmosses , firmosses , spikemosses and quillworts . They have dichotomously branching stems bearing simple leaves called microphylls and reproduce by means of spores borne in sporangia on the sides of the ...