Final answer:
Ferns are the most advanced seedless vascular plants, while whisk ferns lack both roots and leaves. The most diverse group of seedless vascular plants are ferns.
Step-by-step explanation:
Ferns are considered the most advanced seedless vascular plants and display characteristics commonly observed in seed plants. They form large leaves called fronds and have branching roots. On the other hand, whisk ferns lack both roots and leaves. They perform photosynthesis in the green stem and have small yellow knobs at the tip of the branch stem that contain sporangia. The most diverse group of seedless vascular plants, which include club mosses, horsetails, and ferns, are ferns.