3. Adiantum jordanii Müller Halle, Bot. Zeitung. 1864: 26. 1864.
Stems short-creeping; scales reddish brown, concolored, margins entire. Leaves arching or pendent, clustered, 30--45 cm. Petiole 1--1.5 mm diam., glabrous, not glaucous. Blade lanceolate, pinnate, 20--24 × 8--10 cm, gradually reduced distally, glabrous; proximal pinnae 3(--4)-pinnate; rachis straight, glabrous, not glaucous. Segment stalks 1--4 mm, with dark color ending abruptly at segment base. Ultimate segments fan-shaped, not quite as long as broad; base truncate or broadly cuneate; margins of fertile segments unlobed but very narrowly incised, sterile segments with margins lobed, denticulate; apex rounded. Indusia transversely oblong, 3--10 mm, glabrous. Spores mostly 40--50 µm diam. 2 n = 60 .
Sporulating early spring--midsummer. Seasonally moist, shaded, rocky banks, canyons, and ravines; 0--1000 m; Calif., Oreg.; Mexico in Baja California.
Adiantum jordanii occasionally hybridizes with A . aleuticum where their ranges overlap in northern California, yielding the sterile hybrid Adiantum × tracyi C. C. Hall ex W. H. Wagner. Adiantum × tracyi , morphologically intermediate between its parental species, can be distinguished from A . jordanii by its broadly deltate leaf blade that tapers abruptly from the 4(--5)-pinnate base to a 1-pinnate apex. It is best separated from A . aleuticum by leaf blades with a strong rachis, and by ultimate blade segments that are less than twice as long as broad. Adiantum × tracyi shows 59 univalents at metaphase; its spores are irregular and misshapen (W. H. Wagner Jr. 1962).