Selaginella and Salvinia are considered to represent a significant step towards evolution of seed habit because

Step-by-step solution

Selaginella and Salvinia are heterosporous as they produce two kinds of spores-mirco (small) spores and macro (large) spores. The microspores and megaspores germinate and give rise to male and female gametophyte, respectively. The female gametophyte in these plants are retained on the parent sporophytes for variable periods. The development of the zygotes into young embryos takes place within the female gametophytes. This event is the precursor to the seed habit considered to an important step in evolution.