Final answer:
Ferns are the most abundant group of seedless vascular plants with over 20,000 species. They are known for large leaves called fronds, thrive in moist and shaded areas, and reproduce via spores.
Step-by-step explanation:
The most abundant group of seedless vascular plants are ferns, with an estimate of more than 20,000 species existing worldwide. These species vary widely in form, but most share common structural characteristics like large leaves known as fronds and sori contained on the undersides of the fronds. Seedless vascular plants, which also include club mosses, whisk ferns, and horsetails, reproduce through spores and are significant components of Earth's vegetation. Ferns in particular thrive in moist and shaded locations, although they can be found in a range of environments from the tropics to temperate forests.
Although some species can survive in dry environments, most ferns are restricted to moist and shaded places. Ferns made their appearance in the fossil record during the Devonian period and expanded during the Carboniferous period.