Tree species are limited to dwarf species like Arctic willow, Alaska willow and dwarf birch. Within the tundra, some dominant plant species include lichen, cotton grass, and Arctic willow. The Arctic willow is a food source for several Arctic animals. The breeding range extends north of the treeline into low Arctic willow and alder beds. Salix arctica, the Arctic willow, is a tiny creeping willow (family Salicaceae). These include Arctic willow, crowberry, sedges, mosses and lichens. The Arctic willow may be up to around horizontally, but only tall. The Arctic willow is the only woody species to grow on Ellesmere Island. The Arctic willow, commonly named rock willow, is found in the North American tundra. Dwarf scrub heath, dwarf birch, Arctic willow, well-drained lichens, and herb vegetation dominate the flora. Arctic willow ("Salix arctica") is tiny, creeping, prostrate, and mat forming.