![]() ![]() 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. Disruptive selection within species resulted in there being two separate sexes of gamete or even the whole plant. Heterospory and separate sporangia probably evolved in response to competition for light. During the Devonian period there were many species that utilized vertical growth to capture more sunlight. It is proposed that the emergence of heterosporous plants started with the separation of sporangia, which allowed for the development of two different spore types numerous small spores that are easily dispersed, and fewer, larger spores that contain adequate resources to support the developing seedling. Heterosporous plants, similar to anisosporic plants, produce two different sized spores in separate sporangia that develop into separate male and female gametophytes. Heterospory evolved due to natural selection that favoured an increase in propagule size compared with the smaller spores of homosporous plants. ![]()
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