Question

Name two examples of heterosporous pteridophytes.

Answer 1

Hint: Spores are units of plants that help in reproduction. Spores are haploid entities formed in sporangium. Spores are of two types – megaspore and microspore.

Complete answer:
Heterosporous plants are the plants that form two types of spores – microspores and megaspores. Microspores are the male gametes while megaspores are the female gametes. The phenomenon of producing two types of spores is called heterospory. Microspores are developed within the microsporangia and are smaller spores. Megaspores, similarly, are developed within the megasporangia and are larger in size compared to the microspores.
Heterospory was first studied in pteridophytes and is believed to have been originated during the Devonian period. Pteridophytes are also known as cryptogams. This is because they reproduce with the help of spores and do not have visible reproductive organs. These plants show alternation of generation, that is a diploid sporophyte produces gametes in the form of haploid spores which in turn forms a diploid sporophyte. The Pteridophytes are primarily homosporous, that is they produce similar spores rather than producing microspores and megaspores. However, there are certain species of Pteridophytes that exhibit heterosporphy. Typical heterosporous Pteridophytes are Selaginella and Salvinia.

Note: Homospory and Heterospory are the phenomenon of producing similar or dissimilar spores. Heterosporous plants produce two types of spores – male and female. The two types of spores fertilize resulting in the formation of zygote that eventually forms a new plant. Heterospory is considered to be an important evolutionary phenomenon associated with the seed habit. The retention of megasporangium ensures that the zygote is well nourished and develops into a viable sporophyte.