Tundra is treeless vegetation found at high elevation in mountains and in many landscapes of the Arctic. Collectively, ecosystems with tundra vegetation are grouped into the tundra biome. A distinction is usually made between Arctic tundra, which exists beyond the northern limit of tree growth, and alpine tundra, which exists above the elevational limit of tree growth in mountains. In mountains of the far north this distinction becomes blurred as tree lines descend to meet the northern limits of trees. Tundra is dominated by low-growing, perennial angiosperms and by mosses and lichens. Larger plants include grasses, sedges, herbs, and dwarf shrubs, but it is the lack of trees that most characterizes tundra. Plant species commonly found in tundra include sedges; grasses, including many of the genus Poa; willows, blueberries, dwarf birch, and other deciduous and evergreen shrubs or other low-growing woody plants; a host of herbaceous perennials, including...