Practice question

Marsilea, aquatic clover-like fern with four-lobed sporocarps enclosing sori, and Salvinia, floating fern with bilobed leaves, are heterosporous leptosporangiate ferns belonging to order Salviniales. They produce two distinct sporangial types within sporocarp: microsporangia containing many microspores developing into male gametophytes, and megasporangia each containing single large megaspore forming female gametophyte providing nutrients to embryo. Most ferns are homosporous, roots persist functionally, homospory ancestral, seed formation absent. Heterospory in these aquatic ferns demonstrates convergent evolution toward seed habit similar to Selaginella.