Which is the most diverse group of seedless vascular plants?
the liverworts
the horsetails
the club mosses
the ferns

The most diverse group of seedless vascular plants are the ferns .

Explanation:

Ferns -

Ferns are the most advance seedless vascular plants and is the most diverse group . Ferns have branching roots and large leaves . But the whisk ferns , have lack of roots and leaves due to evolutionary reduction . In the process of evolutionary reduction , the natural selection reduces the size of the structure which no longer favors the particular environment . Hence , Photosynthesis in whisk ferns takes place in their green stem .