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Perennial woody vine from a rhizome; stems clambering or climbing, generally to 6 m long (up to 20 m), nearly smooth to densely short stiff-hairy or long soft-hairy; dioecious.
Opposite, pinnately compound, the 5 to 7 leaflets stalked, broadly egg- to lance-shaped, 3-9 cm long,1-7 cm wide, lobed or not, margins entire to coarsely few-toothed, smooth or sparsely soft-hairy on upper surfaces, especially on veins; the stalks persisting, acting as tendrils.
Inflorescences axillary, compound cymes of 7 to 20 flowers on current year's stems, the flowers crowded, unisexual; flower stalks slender, 0.5-3 cm long; petals absent; sepals 4, wide-spreading, white to cream, egg-shaped to oblanceolate, 6-10 mm long, soft-hairy; stamens 25-50, pistillate flowers with sterile stamens; pistils 25-65, staminate flowers without vestigial pistils.
Achenes, elliptic, 3-3.5 mm long, about 1.5 mm wide, silky-hairy; beaks 3-3.5 cm long, feathery-hairy.
Source: The Illustrated Flora of British Columbia