Phylum Pterophyta: Ferns The largest group of living seedless vascular plants—and probably the most familiar—are the ferns with about 12,000 species, over two-thirds of which are tropical. Ferns are an ancient group. Spores and leaf impressions of plants that lived 400 million years ago in the Middle Devonian have been found, but almost all of these early types (grouped simply as “preferns”) were extinct by the Permian. The group to which most modern ferns belong, the Filicales, first appeared in the Lower Carboniferous, 300 million years ago. Characteristics The ferns are an extremely diverse group, and there is no single characteristic that defines them. The following features are present in most: • Leaves, called fronds , are megaphylls . Most are compound with a rachis and numerous pinnae (or compound once again with pinnules). Almost all have
This is the end of the preview. Sign up
access the rest of the document.