bluegrass, any species of the large and widely distributed genus Poa, chiefly range and pasture grasses of economic importance in temperate and cool regions. In general, bluegrasses are perennial with fine-leaved foliage that is bluish green in some species. One of the best known and most important is the sod-forming Kentucky bluegrass, or June grass ( P. pratensis ), believed to have been introduced from the Old World and now widely naturalized in the United States; Kentucky is known as the Bluegrass State because this species is so prevalent there. Others are rough bluegrass ( P. trivialis ), used for shady lawns; Sandberg bluegrass ( P. secunda ), the most common native species; and big bluegrass ( P. ampla ), an important range grass. Bluegrass is classified in the division Magnoliophyta, class Liliopsida, order Cyperales, family Gramineae.