In most of the West, Salix planifolia
is a high elevation species, found in a variety of mountainous habitats; its range extends to Canada and Alaska, and it occurs progressively closer to sea level further north. Plants vary greatly in height depending on the environment, from less than 1 foot to over 30. Young twigs are dark purple to nearly black; older branches are light grey. Leaves, appearing after the flowers, are usually entire, with shiny, dark green upper surfaces, and grey-green below, glabrous or finely hairy. Leaves have lighter-coloured venenation, the side veins not quite reaching the margin.
Staminate flowers have greenish filaments and red-purple anthers, later turning yellow, and a covering of silky white hairs, longer than the stamens. Pistillate flowers are bright green, ascending, in a cluster of 3 inches, around twice as long as the staminate catkins.