Adiantum (maidenhair fern) is a genus of about 200 species of ferns in the familyPteridaceae, though some researchers place it in its own family, Adiantaceae. The genus name comes from the Greek, meaning "not wetting", referring to the fronds' ability to shed water without becoming wet.
They are distinctive in appearance, with dark, often black stipes and rachises, and bright green, often delicately-cut leaf tissue. The sori are borne submarginally, and are covered by reflexed flaps of leaf tissue which resemble indusia. Dimorphism between sterile and fertile fronds is generally subtle.
They generally prefer humus-rich, moist, well-drained sites, ranging from bottomland soils to vertical rock walls. Many species are especially known for growing on rock walls around waterfalls and water seepage areas.
The highest species diversity is in the Andes in South America. Fairly high diversity also occurs in eastern Asia, with nearly 40 species in China.
Two species are commonly native to the eastern United States, with one of these common to western Europe. The Five-finger fern (Adiantum pedatum) is a distinctively American species, with a highly distinctive frond form and a bifurcating frond that radiates pinnae on one side only (see photo in taxobox). It grows from subarctic North America into the deep south of the U.S. A closely related species, A. aleuticum, has been separated from A. pedatum, and grows in northwestern North America and northeast Asia. The other American species, which also grows in Europe, is the Venus-hair fern (Adiantum capillus-veneris). This fern is strictly a southern species in the U.S., and in Europe is confined to the mild, humid Atlantic fringes, including the west of the British Isles. A species in the western United States, specifically California, is California Maiden Hair (Adiantum jordanii).
There is a rich Adiantum flora in New Zealand with 3 endemic species (A. cunninghamii, A. viridescens and A. fulvum) in a total of 10 recorded species. Many of these are common especially in the west and south of the islands.
Horticulture
Many species are grown in the horticultural trade, including all three of the species mentioned, as well as a number of tropical species, including A. raddianum and A. peruvianum. Both A. pedatum and A. aleuticum are hardy to zone 3, and are by far the most cold-hardy members of the genus. A. venustum is also cold-hardy to zone 5. A. capillus-veneris is hardy to zone 7.
