A vigorous, deciduous climber, with twining, downy stems, 10 ft or more high. Leaves heart-shaped, rounded or blunt-pointed at the apex, 3 to 8 in. long, nearly as wide; downy on both sides; stalk downy, 1 to 2 in. long. Flowers solitary on slender, downy stalks 1 in. long, with a tiny ovate bract at mid-length. Perianth tubular, inflated, about 2 in. long, bent double, about 3⁄4 in. wide at the bend; downy, slightly contracted at the mouth, where are three slightly expanding lobes, dull purple.
Native of California; introduced to Kew in 1877 by Sir Joseph Hooker, who had collected it at Chico. In foliage it is similar to A. tomentosa, the leaves remaining downy until they fall, but not so markedly so. The flower, too, is less downy, larger, broader, and more inflated. A. macrophylla differs from both in its smooth flowers, with a large bract on the stalk.