A group of approximately 100 species of grass; more than 30 are represented in the United States. Tall fescue (Festuca arundinacea), a perennial cool-season plant introduced from Europe, occupies about 35×10⁶ acres (15×10⁶ hectares), primarily in the humid south-central region of the United States. It is popular because of its ease of establishment, vigor, wide range of adaptation, long grazing season, tolerance to abuse, sufferance of drought and poor soils, pest resistance, good seed production, and esthetic value when used for turf, ground cover, and conservation purposes. Its dominance of pastures and roadsides indicates that it fills an important ecological niche. It is used primarily as pasture and hay for beef cattle, with lesser use for dairy cows or replacement heifers, sheep, and horses. The leafy and vigorous plants can grow to 3–4 ft (0.9–1.2 m) if undisturbed; under grazing or clipping, they can form a dense sod when sufficient water and fertility are available.