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Heterosporangium: A new category of sporangium in Lycopsida

Publication Type:Journal Article
Year of Publication:2014
Authors:H. Goswami
Journal:Acta Botanica Hungarica

This is being hypothesised that the heterospory to begin with, might have originated within one specific sporangium thereafter separate male and female sporangia would have evolved in due course of time. This new category of a sporangium, is hereby named as "heterosporangium", conceived to have been the cradle sporangium for the origin of heterospory. Such a sporangium may have possessed three types of spores, viz. microspores, megaspores and morphologically distinct spores possessing resemblances with spores of past lineages/fossils. Such a classical structure has been exemplified by a fundamental discovery of "intrasporangial heterospory" in 1968. This appears that this evolutionary phase could have followed the path of sequential evolution of isosporangium-anisosporangium-heterosporangium and finally, leading to "intersporangial heterospory" in the form of independent microsporangium and megasporangium. The independent sex differentiated sporangia must have had evolved by selective degeneration of spore mother cells in a differentiating young heterosporangium. In other words, a microsporangium should have evolved by the degeneration of megaspore mother cells and megasporangium by early degeneration of microspore mother cells. This selective degeneration must have been operative on account of some genetic mechanism as suggested by Bell in 1996 and later, demonstrated by our observations on epigenetic mechanisms suspecting mainly abrupt hypomethylation of DNA, to be responsible event as indicated in heterosporangia of Isoetes pantii Goswami et Arya. This paper exclusively establishes heterosporangium as a structure of rare evolutionary importance genetically inherent within the genome of the species observed consistently for more than five decades. Recent decline of such plants of I. × pantii does not lower down importance of heterosporangium because its physical presence can never be denied. The future of a species or an organ depends on operative modes of natural selection.

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