Prepare a detailed account on heterospory under the headings – definition, two examples, incipient heterospory, biological significance, and evolution of seed habit.

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 arborescent horsetails, and progymnosperms. This occurred as part of the process of evolution of the timing of sex differentiation.

Heterospory developed due to natural selection pressures that encouraged an increase in propagule size. This may first have led to an increase in spore size and ultimately resulted in the species producing larger megaspores as well as smaller microspores.

Heterospory evolved from homospory many times, but the species in which it first appeared are now extinct. Heterosporic plants that produce seeds are their most successful and widespread descendants. Seed plants constitute the largest subsection of heterosporic plants.

Heterospory in Pteridophytes:

Most of the Pteridophytes produce one kind of similar spore. Such Peridophytes are known as homosporous and this phenomenon is known as homospory. However, there are some Pteridophytes which produce two ________ ____ ____ ____ ______ _____ ___ _________ ___.
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