A deciduous climbing shrub up to 25 or 30 ft high; young shoots glabrous but becoming conspicuously marked with elongated lenticels; pith chambered. Leaves oval, ovate or oblong, finely and regularly toothed, with a short slender point and a rounded or wedge-shaped base; 3 to 5 in. long, 11⁄2 to 21⁄2 in. wide; glabrous on both surfaces; stalk 1 to 2 in. long. Flowers white or creamy yellow, 1⁄2 to 4⁄5 in. wide, fragrant, solitary to as many as five together, borne on glabrous slender stalks; anthers yellow; ovary downy. Fruit egg-shaped to oblong, 3⁄4 to 1 in. long, green tinged with red, spotted.
Native of N. India, described and named as long ago as 1836 by Lindley and found by such early collectors as Griffiths in Bhutan, Wallich in Nepal, and Hooker in Sikkim; also of W. China, where it has been collected by Henry and Forrest. S. T. Dunn, a leading authority on the genus, observes that it may be distinguished by its yellow anthers, downy ovary, and spotted fruits.
A number of species closely related to A. callosa have been described, but so far as is known, only one has been introduced. This is A. venosa Rehd., which differs from that species in the rusty down that covers the sepals and inflorescence, and the prominently net-veined leaves.
† A. rubricaulis Dunn – One of the many allies of A. callosa, this has been in cultivation at Kew since 1924, raised from seeds sent from China by Y. Chen. It is a vigorous, glabrous climber with purple, lenticellate shoots. Leaves up to 4 in. long and 11⁄4 in. wide, lanceolate to oblong-ovate, acuminately tapered at the apex, rounded at the base, finely toothed. Flowers and fruits smaller than in A. callosa.