Question

Is Psilotum homosporous or heterosporous?

Answer 1

The difference between heterosporous and homosporous pteridophytes lies in the size of their spores. The heterosporous pteridophytes produce megaspores as well as microspores while homosporous pteridophytes produce only homosporous that are of the same size.

Complete answer:
Pteridophytes are considered as an intermediate between primitive and higher plants. Most of them exhibit homospory, but some of them do exhibit heterospory. Homospory refers to the condition where plants produce one type of spore. Heterospory refers to the condition where plants produce two different kinds of spores namely microspore and megaspore. The microspores are small and are male and the female megaspore is large in size.
The major structural difference among the heterosporous and homosporous pteridophytes lies in the size of their spores and this is evident from the fossil records as well. The smaller spores are produced inside the microsporangia and are known as microspores. These germinate to give rise to the male gametophyte. The larger spores develop inside the megasporangia and are known as megaspores. These germinate into the female gametophyte.

Psilotum is a fern with synangia formed by the fusion of three sporangia that bear the spores. The spores are of similar structure and hence they are homosporous. The spores germinate to form the gametophyte.

Note:
Homospory refers to the condition where plants produce one type of spore. Heterospory refers to the condition where plants produce two different kinds of spores namely microspore and megaspore. The microspores are small and are male and the female megaspore is large in size.