Adiantum aleuticum

Formerly included in Adiantum pedatum (under various names including A. pedatum var. aleuticum and A. pedatum var. calderi), but reproductively and morphologically isolated (C.A. Paris, Flora of North America, vol. 2, 1993). Accepted as a species by Kartesz (1994 checklist and 1999 floristic synthesis). Widespread but somewhat irregularly distributed in the American West, from Arizona, California, and Chihuahua north to Montana, Alberta, and Alaska; also occurring infrequently, primarily or exclusively on serpentine, in the northeastern U.S. and southeastern Canada. The true Adiantum pedatum (as presently interpreted) is eastern, ranging westward only to Minnesota, Nebraska, and Texas (see maps in Flora North America, vol. 2, 1993).

Aleutian Maidenhair Fern (Adiantum aleuticum) occurs in western North America, from the Aleutian Islands, and Pacific coastal Alaska, south to California, and Idaho, with disjunct locations in Utah, Wyoming, Colorado, Arizona, northern Mexico, northern New England, southern Quebec, and Newfoundland. It is estimated that there are more than 3000 occurrences.

Aleutian Maidenhair Fern (Adiantum aleuticum) occurs in western North America, in the United States and Canada, from the Aleutian Islands, and Pacific coastal Alaska, south to California, and Idaho, with disjunct locations in Utah, Wyoming, Colorado, Arizona, northern Mexico, and eastern North America, in northern New England, southern Quebec, and Newfoundland, Canada. It does not occur in Maryland. Range extent was estimated to be 14.2 million square kilometers using herbarium specimens and photo-based observations documented between 1992 and 2023 (Ackerfield 2015, GBIF 2023, iNaturalist 2023, Knapp and Naczi 2021, Nelson and Legler 2023, Villaseñor 2016, Windham 1993).

By applying a 1 km separation distance to herbarium records and photo-based observations documented between 1992 and 2023, it is estimated that there are more than 3000 occurrences rangewide (GBIF 2023, iNaturalist 2023).