- Family: Willow Family – Salicaceae
- Subspecies: Ssp. lanata, Ssp. glandulifera
- Growing form and height: Shrub. 0.8–1 m (2.5–3.3 ft.).
- Flower: Male and female flowers on separate plants. Inflorescence a short-stalked, erect catkin, shining white-woolly, golden-hairy in young male plants. Individual flowers in axils of catkin scales, small, lacking perianth. Catkin scales sharp-pointed, deep brown, and long-hairy. Stamens 2, filaments long hairless, anthers golden yellow. Pistil formed from 2 fused carpels, style long, tapering, yellowish-green.
- Leaves: Alternate. Stalked, stipulate. Stipules small, ovate, entire, soon falling. Leaf-blade entire, 5–8 cm (2–3.2 in.) long, roundish obovate to oval, downy on both sides, with prominent veins beneath. Vein pairs 8–10.
- Buds: Yellowish-brown, grey-hairy.
- Fruit: Fairly slender, hairless capsule. Seeds plumed.
- Habitat: Snowy areas on fjelds, damp slopes and depressions, meadows, streamsides, river margins, shores. Rarely an ornamental. Often on calcareous soil (is calciphile).
- Flowering time: May–June. Flowers before coming into leaf.
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. Hybrids between willow species are common.
Woolly willow is one of the ‘grey-willows’ of the Lappish fjelds, the two others being gray willow and downy willow (S. glauca and S. lapponum). Woolly willow is a demanding fjeld and tundra species that flowers in the spring before coming into leaf. Its stout, spreading brown branches are densely woolly especially when young. Woolly willow’s subspecies glandulifera has gland-fringed leaves, and large, persistent, gland-fringed stipules.