Rhizomes horizontal, shallow, internodes (0.5-)1.5-6.5 cm. Leaves: petiole 7.5-17 cm, sparsely crisped-hirsute. Leaf blade not variegate, cordate, 3-8.5 × 4.5-12 cm, apex usually obtuse, occasionally broadly acute; surfaces abaxially sparsely appressed-hirsute, at least proximally, adaxially glabrous or sparsely appressed-hirsute, marginal hairs perpendicular to margin or curved toward apex. Flowers horizontal; peduncle 1.5-5 cm; false calyx tube cylindric, externally brown-purple, rarely greenish, hirsute, internally white, usually with median purple stripe, with usually purple, rarely white hairs; distal portion of sepal spreading or weakly (rarely strongly) reflexed at anthesis, (11-)30-75 mm, apex filiform-attenuate, abaxially purple or greenish, sparsely hirsute, adaxially purple, puberulent with crisped purple hairs; pollen sacs 1.5-2 mm, sterile tip of connective on inner stamens purple, 0.5-1 mm, shorter than pollen sacs. 2 n = 26.

Flowering spring-summer (Apr-Jul). Understory of conifer forests, usually in mesic or wet places; 0-1200(-2200) m; B.C.; Calif., Idaho, Mont., Oreg., Wash.

In most populations of Asarum caudatum , the distal portion of the sepal is spreading or weakly reflexed and 30-75 mm. A single population south of Mt. Shasta, California, has the distal sepals strongly reflexed and unusually short, often as little as 1.1 cm. Flowers of these plants superficially resemble those of A . lemmonii ; they differ in being horizontal, not descending as in A . lemmonii , and in the filiform-attenuate sepals.

Native Americans used Asarum caudatum medicinally to treat headaches, intestinal pain, knee pain, indigestion, boils, tuberculosis, and colic, and as a general tonic (D. E. Moerman 1986).