Salix arbusculoides is a narrow-leafed tall shrub, typically found along streams and in moist forests in Denali's lowland boreal region. Plants grow 1-6 m tall with fine, smooth reddish twigs and branches. Leaves are long, narrow, glossy green, silky underneath, with finely serrated margins (with minute gland-tipped serrations) and no stipules. Willows are dioecious (separate plants produce either male or female flowers); the flowers highly reduced and borne in catkins specialized for wind pollination. Female catkins appear with the leaves and are short (~5 cm) and loosely flowered, without elongate stipes. Pistils are covered with silky hairs. The fruits are capsules, sparsely covered in gray hairs, opening by two valves to release seeds. This is one of several species of willow that can form 'diamond willow' when under attack by a canker. The smooth reddish twigs, lack of stipules, hairy catkins and narrow, serrated leaves with gland-tipped teeth help identify this willow.
Catkins and leaves (which develop together) develop mid-May. Seeds are released by mid-June (Collett 2004).
Salix arbusculoides is dioecious, and insect and wind pollinated. Seeds have attached hairs to aid in wind dissemination. It can also spread vegetatively by underground rhizomes and roots. Broken branches also can readily root to establish new plants.
Collett (2004) documented a variety of insects that utilize S. arbusculoides including gall-formers such as: Rabdophaga spp., Euura sp., Pontia sp., and eriophyid mites, and a leaf mining moth, Micrurapteryx salicifoliella. ""Diamond willows"" also form with this species, which is caused the canker fungus Valsa sordida. Another fungus, Rhytisma salicinum causes tar spots on leaf surfaces.
Salix arbusculoides has a wide variety of traditional uses as medicine and construction materials. Like all willows, the fresh bark of S. arbusculoides contains salicin, a precursor to aspirin and has traditionally been used as pain and fever reliever. Willow suckers (long straight branches) have long been utilized for constructions of baskets, arrow shafts, crab pots, fish traps, furniture and other objects. S. arbusculoides has been used for streambank restoration as cuttings can be directly planted and take root.
Salix arbusculoides is endemic to northern North America, ranging from Alaska across northern Canada to Quebec. It does not occur in the continental United States. In Alaska, S. arbusculoides occurs across the state except is absent or very rare in coastal southcentral Alaska, the Aleutians and the southeastern panhandle. In Denali, S. arbusculoides occurs primarily north of the Alaska Range, but there are also a few widely scattered stations for the species on the south side.
Salix arbusculoides is primarily a lowland boreal forest species. In Denali, it is observed from 156 m to 1145 m, with an average plot elevation of 428 m. It seems to slightly prefer north-facing slopes, but does not show strong preference in slope angle.