Ferns are the most abundant of the (seedless vascular/seedless nonvascular)plants.

Answer: Seedless vascular

Explanation:

Vascular plants are the ones which have xylem and phloem for conduction of water and minerals and food respectively. Xylem and phloem are termed as vascular tissues and hence, the name.The principal generation phase in vascular plants is termed as a sporophyte and they also have true root, stem and leaves.Several groups of plants that fall under the category of vascular plants are horsetails, ferns, club-mosses, gymnosperms and angiosperms.Ferns are considered to be vascular plants as they have as they have specialised conducting tissues i.e xylem and phloem, they have branched stems and sporophyte is the dominant phase in their life cycle.Further, they also have complex leaves which are called as megaphylls.Ferns are termed as seedless because they use spores for reproduction and thus, they do not produce any flowers or seeds.Thus, ferns are the most abundant of seedless vascular plants .