Poa pratensis, commonly known as Kentucky bluegrass, smooth meadow-grass, or common meadow-grass, is a perennial species of grass native to Europe, Asia, North America, and northern Africa. Poa pratensis forms a valuable pasture plant, characteristic of well-drained, fertile soil. It is also used for making lawns in parks and gardens and is common in cool moist climates like the northeastern United States.
Poa pratensis was one of the many species described by Carl Linnaeus in his landmark work Species Plantarum in 1753. Poa is Greek for fodder and pratensis is Latin for meadow. The name Kentucky bluegrass derives from its flower heads, which are blue when the plant is allowed to grow to its natural height of two to three feet.
Poa pratensis is the type species of the grass family Poaceae.
There are two ill-defined subspecies:
Poa pratensis is a herbaceous perennial plant 30-70 centimetres (12-28 in) tall. The leaves have boat-shaped tips, narrowly linear, up to 20 centimetres (8 in) long and 3-5 millimetres (0.12-0.20 in) broad, smooth or slightly roughened, with a rounded to truncate ligule 1-2 millimetres (0.039-0.079 in) long. The conical panicle is 5-20 centimetres (2-8 in) long, with 3 to 5 branches in the basal whorls; the oval spikelets are 3-6 millimetres (0.12-0.24 in) long with 2 to 5 florets, and are purplish-green or grey. They are in flower from May to July, compared to annual meadowgrass (Poa annua) which is in flower for eight months of the year. Poa pratensis has a fairly prominent mid-vein (center of the blade).
The ligule is extremely short and square ended, making a contrast with Annual Meadowgrass (Poa annua) and Rough Meadowgrass (Poa trivialis) in which it is silvery and pointed. The Kentucky bluegrass is a dark green compared to the apple green color of poa annua and poa trivialis.
The rootstock is creeping, with runners (rhizomes). The broad, blunt leaves tend to spread at the base, forming close mats.
This species is among the foodplants of the caterpillars of the Meadow Brown (Maniola jurtina) and Gatekeeper (Pyronia tithonus) butterflies; the Common Sun Beetle (Amara aenea) (adults feed on the developing seeds), Eupelix cuspidata of the leafhopper family, and Myrmus miriformis, a grassbug (feeds on young blades and developing seeds).
Since the 1950s and early 1960s, 90% of Kentucky Bluegrass seed in the United States has been produced on specialist farms in Idaho, Oregon and Washington.
During the 1990s botanists began experimenting with hybrids of Poa pratensis and Texas bluegrass (P. arachnifera), with the goal of creating a drought and heat-resistant lawn grass.