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. 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; 0--1800 m; B.C., N.W.T., Yukon; Alaska. Cryptogramma sitchensis is an allotetraploid species (2 n = 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.