From similarity of physical circumstances the arctic flora of America bears a strong resemblance to that of the northern regions of Europe and Asia. This botanical district comprises Greenland, and extends considerably to the south of the arctic circle, especially at the eastern and western ends of the continent, where it reaches the 60th parallel of N. lat., and even more; it is continued along the tops of the Rocky Mountains almost to Mexico, and it re-appears on the White Mountains and a few other parts of the Alleganies.

Greenland has a much more arctic flora than Iceland; the valleys are entirely covered with mosses and marsh plants, and the gloomy rocks are cased in sombre lichens that grow under the snow, and the grasses on the pasture grounds that line the fiords are nearly four times less varied than those of Iceland. In some sheltered spots the service-tree bears fruit, and birches grow to the height of a few feet; but ligneous plants in general trail on the ground.

The arctic flora of America has much the same character with those of Europe and Asia, and many species are common to all; still more are representative, but there is a difference in the vegetation at the two extremities of the continent; there are 30 species in the east and 20 in the west end which grow nowhere else.