Fern
Fern is a common name for any of a division of cryptogamous (spore-producing) plants. The fern phylum contains about 150 genera; estimates of the number of species range from 6000 to 15,000. Ferns are found throughout the world. Most grow in damp, shady places, although certain species grow on dry ground, soil, or rocks. Some ferns, in fact, grow only in rocky places—in fissures and crevices of cliff faces and in boulders. Others grow as epiphytes, or air plants, on trees. Fossil remains of ferns have been found in rocks of the Lower Devonian Period. The phylum thus appeared on earth earlier than any seed-bearing plants. Ferns are among the oldest land plants. Ferns vary in size from those only a few centimeters high to the tree ferns of tropical regions, which may reach a height of 24 m (80 ft). Tree ferns have woody trunks without branches, topped with clusters of feathery leaves, or fronds. Most ferns, however, have no trunks, and fronds grow directly from a short underground stem.