General:
Deciduous perennial, palmately branched, from a stout, scaly rhizome, 15-75 cm tall.

Leaves:
Broadly fan-shaped, 10-75 cm long; stalks reddish-brown to purplish-black; blades more or less palmately-pinnate, set at right angles to the stalks and more or less parallel to the ground, 10-40 cm long, 10-40 cm wide, rounded to kidney-shaped, forked at the bases into 2 recurved-spreading divisions which in turn bear 2-several shorter divisions, the larger divisions with 15-35, alternate, short-stalked

Notes:
Small plants with small fronds (5 to 15 cm across) and strongly overlapping ultimate segments were described as A. pedatum L. var. subpumilum Wagner. They clearly belong to this species, but no formal nomenclatural transfer has been done yet. This variety is rare on coastal bluffs from northern Vancouver Island south to the Olympic Peninsula, WA.

Source:  The Illustrated Flora of British Columbia