- Subspecies: Ssp. myrsinifolia, Ssp. borealis, Ssp. kolaênsis
- Family: Willow Family – Salicaceae
- Growing form and height: Shrub or small tree. 2–5 m (7–16 ft.).
- Flower: Male and female flowers on separate plants. Inflorescence an erect catkin on a short, spreading, small-leaved stalk. Individual flowers in axils of catkin scales, small, lacking perianth. Catkin scales narrowly elliptic, hairy, with dark tip. Stamens 2, base of filament hairy, anthers yellow. Pistil formed from 2 fused carpels, ovary long-stalked, hairy.
- Leaves: Alternate. Short stalked, stipulate. Stipules large, ovate to kidney-shaped, margins finely glandular-serrate. Leaf-blade 4–8 cm (1.6–3.2 in.) long, elliptic to ovate or oblong, sometimes obovate, shallowly saw-toothed, almost hairless, sparsely hairy when young, green and glossy above, dullish beneath. Vein pairs 6–8(–11).
- Buds: With blunt apex, hairy.
- Fruit: Slender, hairless capsule. Seeds plumed.
- Habitat: Shores, spruce swamps, wet ditches, margins of fields and pastures.
- Flowering time: May–June. Flowers just before coming into leaf (ssp. myrsinifolia) or soon after (ssp. borealis and ssp. kolaênsis)
Willows are insect-pollinated, sympodially growing, dioecious trees, shrubs, or dwarf shrubs. Their buds have a single protective scale, and their leaves are entire and stipulate. The inflorescence is a catkin which falls off in one piece.
Dark-leaved willow is a fairly demanding tall shrub or small tree which flowers before coming into leaf. The older twigs are greenish or reddish-brown, slightly glossy, almost hairless. The young shoots are hairy. The common name ´dark-leaved willow´ apparently derives from the fact that the leaves turn blackish when dried. The northern subspecies borealis somewhat resembles the actual dark-leaved willow but differs in being usu. taller and tree-like, having long-haired twigs and leaves, and usu. flowering only after having come into leaf. Still more norther subspecies is kolaënsis. Hybrids between willow species are common. Dark-leaved willow crossbreeds commonly with tea-leaved willow (S. phylicifolia), whortle-leaved willow (S. myrsinites), grey willow (S. cinerea), eared willow (S. aurita) and gray willow (S. glauca).