Botanists, scientists who study plants, generally consider ferns as relatively primitive members of the plant kingdom. Plants that reproduce by flowering and seeding are evolutionarily more advanced than spore-producing plants like ferns. Some ferns have leaves or fronds that are entire. Most, however, feature leaves divided into leaflets. Several fern families with representatives native to the United States provide examples of ferns.
Although ferns are not flowering plants, one family of ferns (Osmundaceae) has earned the moniker "flowering ferns." Ferns in this group produce spore-bearing structures that may resemble flowers that have withered and turned brownish. An example of a fern in this group is the cinnamon fern (Osmunda cinnamomea). It is hardy in U.S. Department of Agriculture plant hardiness zones 3 through 9. The royal fern (Osmunda regalis), hardy to USDA zones 3 through 9, is another of the flowering ferns.
Another fern family (Polypodiaceae) carries an apt name based on the number and shape of its leaflets. Each of the leaflets in this group of ferns is shaped like a foot or a stocking, and these ferns have many leaflets. The family name, based on Greek word roots meaning “many-footed,” refers to this feature. The American wall fern (Polypodium virginianum), hardy to USDA zone 3, is a prime example of the ferns in this group. Another is the resurrection fern (Polypodium polypodioides), hardy to USDA zones 6 through 9.
The so-called filmy ferns are specialized in their habitat requirements and rare. The Appalachian bristle fern (Trichomanes boschianum), hardy to USDA zone 5, is a representative of this group. It grows generally in cave or watery cliff habitats in a handful of states from the midwest to the south. Another example is the lined bristle fern (Trichomanes lineolatum), native to southern Florida and hardy to USDA zone 10b. Other members of this group occur in the tropics.
Although not as rare as the filmy fern in the United States, the American climbing fern (Lygodium palmatum) is another less common fern. It represents the family Lygodiaceaeone, which has more representatives in the tropics than in North America. The American climbing fern, hardy to USDA zone 4, is essentially a vine. It has palmate, or hand-shaped, leaves and a climbing stem and growth habit. Also in this family is the small-leaf, or Old World climbing fern (Lygodium microphyllum), hardy to USDA zone 9b. It is not native to the United States and has become invasive in southern Florida.