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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 ...
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.
In seed plants, the gametophyte is even more reduced (at the minimum to only three cells), gaining all its nutrition from the sporophyte. 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 ...
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.
Like other ferns, members of the Marsileaceae produce spores, but not seeds when they reproduce. Unlike other ferns, the spores in this family are produced inside sporocarps. These are hairy, short-stalked, bean-shaped structures usually 3 to 8 mm in diameter [1] with a hardened outer covering. This outer covering is tough and resistant to ...
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 ...
Curled up Selaginella tamariscina Wallace's Selaginella (Selaginella wallacei). Selaginella, also known as spikemosses or lesser clubmosses, is a genus of lycophyte.It is usually treated as the only genus in the family Selaginellaceae, with over 750 known species.
In gymnosperms and flowering plants, the megaspore is produced inside the nucellus of the ovule.During megasporogenesis, a diploid precursor cell, the megasporocyte or megaspore mother cell, undergoes meiosis to produce initially four haploid cells (the megaspores). [1]