Index Fil. 67. 1857.
Stems decumbent to erect, much branched from base, stout, 10–20 mm diam. (including hardened, persistent leaf bases); scales bicolored, dense, broadly lanceolate to linear, to 7 × 2 mm. Leaves densely tufted, green over winter, persistent; fertile leaves erect, 5–25 cm; sterile leaves spreading, 3–17 cm; hairs small, appressed, cylindric, scattered along grooves of petioles and along costae and costules of adaxial blade surface. Petiole dark brown only on proximal 1/8 or less, green to straw-colored distally, 1–2 mm wide, firm and strawlike, not collapsed; scales bicolored or ± concolored, becoming sparse distally. Blade deltate to ovate-lanceolate, somewhat leathery, opaque; sterile blades dimorphic, 2–3-pinnate or 3–4-pinnate, hydathodes only slightly sunken below leaf surface. Segments of less dissected sterile leaves ovate-lanceolate, regularly dentate to incised with 8–16 teeth or lobes; segments of more finely dissected sterile leaves pinnatifid with 4–8 small, obovate lobes, lobe apices acute; segments of fertile leaves ascending, strongly differentiated, linear, 3–10 × 1–3 mm; margins of fertile segments revolute, covering sporangia. Sporangia in sori that coalesce at maturity.
Habitat: New growth produced in spring, spores maturing in late summer. sterile leaves green over winter, senescing 2d spring. Cliff crevices and talus slopes, lowland to alpine
Elevation: 0–1800 m
B.C., N.W.T., Yukon, Alaska.
Cryptogramma sitchensis is an allotetraploid species (2n = 120; E. Alverson, unpubl. data) that arose through hybridization between C. acrostichoides and another species, possibly the eastern Asian C. raddeana Fomin. Past difficulties in clearly distinguishing C. sitchensis from C. acrostichoides can be attributed to the frequent occurrence of sterile hybrids where the ranges of the two species overlap.