The plants in Division Pteridophyta are seedless. These do not multiply by seeds as the plants in Division Spermatophyta.
The life cycle pattern in both Pteridophyta and Spermatophyta is basically same.
Plants in both divisions exhibit alternation of generations . Main plant body represents sporophytic generation and the gametophytic generation is reduced.
The sporophyte reproduces asexually by meispores (n) . The meispores germinate to give rise to gametophytic generation. The gametophyte is haploid . It reproduces sexually by gametes. The Zygote develops into embryo that grows into mature sporophyte.
Thus the sporophytic and gametophytic generatons follow each other in alternate sequence. This phenomenon is termed alternation of generations.
The main difference in Pteridophytes and spermatophytes is that sporophyte in most of the pteridophytes (e.g. ferns) is homosporous; whereas sporophyte in spermatophytes is always heterosporous.**
The gametophyte in ferns is independent, though reduced and is exosporic . In hetrosporous forms there are separate male and female gametopytes. These are reduced and endosporic.
The female gametophyte is reduced and is permanently retained in megasporangium (ovule) and thus embryo formed as a consequence of sexual reproduction is retained inside the ovule permanently. The ovule matures into seed.
Heterspory is the most important evolutionary step that leads to the formation of seed.
The seedless plants (ferns) are homosporous. Some pteridophytes like Sealginella are heterosporous These plants do not produced seeds but show initial steps towards the seed formation.