ABSTRACT
Pteridophytes, Gymnosperms and Angiosperms constitute Tracheophytes, a dominant group of green plants, characterized by the presence of a well developed branched, independent and dominant sporophyte, with a vascular system consisting of xylem (tracheids-hence the name Tracheophytes, vessels in angiosperms) and phloem (sieve elements, sieve tubes in angiosperms). The group evolved nearly 420 million years ago, and is regarded as monophyletic. Pteridophytes, the seedless vascular plants differ from higher Tracheophytes in lacking seed habit and absence of pollen tube, spores developing freely into gametophytes, although few members exhibit heterospory and the reduction of megaspore number to one, forerunner of seed habit.
