Nassella viridula is a species of grass known by the common name green needlegrass. It is native to North America, where it is widespread in western Canada and the western and central United States. It is introduced in parts of eastern North America.This grass forms tufts of stems up to about 1.2 meters tall. It grows from a fibrous root network which may penetrate over 1.5 meters deep in the soil. The leaves are mostly basal. Each is up to 30 centimeters long and tapers to a threadlike tip.