Adiantum aleuticum

(Ruprecht) Paris

Rhodora 93: 112. 1991

Common names: Western maidenhair Aleutian maidenhair adiante des aléoutiennes
Basionyms: Adiantum pedatum var. aleuticum Ruprecht Distr. Crypt. Vasc. Ross., 49. 1845
Synonyms: Adiantum boreale C. Presl Adiantum pedatum subsp. aleuticum (Ruprecht) Calder & Roy L. Taylor Adiantum pedatum subsp. calderi Cody Adiantum pedatum subsp. subpumilum (W. H. Wagner) Lellinger Adiantum pedatum var. subpumilum W. H. Wagner
Treatment appears in FNA Volume 2.
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Stems short-creeping or suberect; scales bronzy deep yellow, concolored, margins entire. Leaves lax-arching to stiffly erect or pendent, often densely clustered, 15–110 cm. Petiole 0.5–3 mm diam., glabrous, often glaucous. Blade fan-shaped to funnel-shaped, pseudopedate, 1-pinnate distally, 5–45 × 5–45 cm; proximal pinnae (1–)2–7-pinnate; rachis straight, glabrous, often with glaucous bloom. Segment stalks 0.2–0.9(–1.3) mm, dark color entering into segment base or not. Ultimate segments oblong, long-triangular, or occasionally reniform, ca. 2.5–4 times as long as broad; basiscopic margin straight to oblique, or occasionally excavate; acroscopic margin lobed, lobes separated by narrow to broad incisions 0.2–3 mm wide; apex acute to obtuse, obtuse apices divided into ± angular lobes separated by sinuses 0.6–4 mm deep, margins of lobes sharply denticulate. False indusia transversely oblong to crescent-shaped, 0.2–3.5(–6) mm, glabrous. Spores mostly 37–47 µm diam. 2n = 58.

Phenology: Sporulating summer–fall.
Habitat: Wooded ravines, shaded banks, talus slopes, serpentine barrens, and coastal headlands (uncommon)
Elevation: 0–3200 m

Distribution

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Alta., B.C., Nfld., Que., Alaska, Ariz., Calif., Colo., Idaho, Maine, Md., Mont., Nev., Oreg., Pa., Utah, Vt., Wash., Wyo., Mexico in Chihuahua.

Discussion

Adiantum aleuticum is disjunct in wet rock fissures at high elevations in Arizona, Colorado, Montana, Nevada, Utah, Wyoming, and Mexico in Chihuahua, and it is disjunct on serpentine in Newfoundland, Quebec, Maine, Maryland, Pennsylvania, and Vermont.

Although the western maidenhair has traditionally been interpreted as an infraspecific variant of Adiantum pedatum, the two taxa are reproductively isolated and differ in an array of morphologic characteristics. Therefore, they are more appropriately considered separate species (C. A. Paris and M. D. Windham 1988). Morphologic differences between A. pedatum and A. aleuticum are subtle; the two may be separated, however, using characteristics in the key. Adiantum aleuticum occurs in a variety of habitats throughout its range, from moist, wooded ravines to stark serpentine barrens and from coastal cliffs to subalpine boulder fields. Although morphologic differences exist among populations in these diverse habitats, they are not consistent. Consequently, infraspecific taxa are not recognized here within A. aleuticum.

References

None.

Lower Taxa

No lower taxa listed.