Flower:

Panicle 1 to 8+ inches (2 to 20+ cm) long with 2 to 5(7) branches at each node, the lowest nodes usually with 5, and spikelets (flower clusters) mostly on the tip half of a branch. Branches are smooth to rough-textured, typically initially spreading to ascending, the open panicle narrowly to broadly pyramidal to egg-shaped. Spikelets are green to purplish when fresh, flattened, lance-elliptic in outline, 3.5 to 6 mm (to ¼ inch) long with 2 to 5 florets; the uppermost floret may be sterile.

At the base of a spikelet is a pair of bracts (glumes) that are both pointed at the tip, awnless, hairless, keeled, rough along the keel, a pair of lateral veins usually obscure, the upper glume 2.5 to 4 mm long, the lower glume usually somewhat smaller. Surrounding a floret is a pair of bracts (lemma and palea), the lemma 2 to 4.3 mm long, pointed at the tip, usually thin and translucent along the edge, keeled, 5-veined, with long white hairs along the keel and marginal veins, the intermediate veins and surface between veins hairless; the palea is somewhat shorter than the lemma, 2-veined, hairless to sparsely hairy. The thickened base of the floret (callus) has a tuft of long, crinkly hairs; the stalk between florets (rachilla) is hairless.

Leaves and stems:

Leaves are mostly basal with 2 to 4 alternate leaves widely spaced along the stem, .4 to 4.5 mm wide, green to blue-green, boat-shaped at the tip, hairless or sometimes sparsely hairy on the upper surface, and the edges flat or rolled in (involute). Along each side of the midvein is a row of what's known as bulliform cells that can look like indented veins, but are much like bladders that expand and contract in response to moisture conditions, and cause the leaves to fold up lengthwise during droughty periods. Stem leaves are mostly erect to ascending, the uppermost leaf ½ to 4 inches (1.5 to 10 cm) long; basal leaves can reach 18 inches (45 cm) long.

The sheath is hairless, rarely sparsely hairy, the edges fused for ¼ to half their length (closed sheath). The ligule (membrane where the leaf blade joins the sheath) is .9 to 3 mm long, rounded or straight across the top edge and lacks a fringe of hairs. The collar (edge where the blade joins the sheath) is often somewhat thickened and pale. Nodes are smooth, the lowest 1 or 2 nodes usually hidden in the sheaths. Stems are unbranched, round to slightly compressed in cross-section, erect or prostrate from the base and rising at a lower node (geniculate), single or multiple from the base forming loose to dense clumps. Plants spread via creeping rhizomes and can form dense mats, the leaves of new shoots flat, folded or rolled in along the edges (involute).

Fruit:

Spikelets dry to light brown, the branches often (not always) contracting and nodding to one side. Individual florets drop away when mature, leaving the glumes behind persisting on the stalk. The grain (seed) is golden to brown.

Notes:

Kentucky Bluegrass is the most common turf grass planted in North America and is ubiquitous in landscapes across Minnesota, which is just sad to me. I travel through rural parts of the state regularly and am always dismayed by the massive turf grass lawns in farm country, and the wasted time, effort and resources required to keep them manicured. Outside of landscape plantings, this species has spread virtually everywhere, including high grade native habitats. Contrary to what its common name suggests, it is not native to Kentucky, but is generally considered originating in parts Europe and Asia, though it appears probable some of its several subspecies are native to parts of North America. Not (likely) Minnesota, in any case.

Poa species are recognized by their (usually) closed sheaths, leaves with boat-shaped tips, and often long, crinkly hairs around the base of the floret (callus). Kentucky Bluegrass is a rather variable species with as many as 6 subspecies, not all of which are universally accepted, but generally it is distinguished by its rhizomatous growth, shoots single or more often clustered forming loose to dense clumps; stem leaves up to 4.5 mm wide; ligules usually less than 3 mm long; sheaths closed for ¼ to half their length; panicle initially open, the branches often contracting and nodding to one side when dry, usually 5 branches (to 7) on the lowest nodes, spikelets along the tip half of a branch; 2 to 5 florets per spikelet; lemmas 2 to 4.3 mm long, 5-veined, long hairs along the lower half of 3 veins, callus moderately to densely covered in long, crinkly hairs.

Three of the 6 subspecies have been recorded in Minnesota (subsp. pratensis, angustifolia, agassizensis), differentiated in part by characteristics of new shoots: whether they emerge erect from the sheath (intravaginal), from the side (extravaginal), or both, plus the width of shoot leaves and whether they are flat, folded, rolled along the edge (involute), or some combination—it's complicated. Among other characteristics, subsp. agassizensis is the smallest, typically with small panicles, ligules are described as shorter and more rounded; subsp. angustifolia is more robust and very similar to subsp. pratensis, which is the most common—the most reliable difference between these two are in the new shoot leaves, not more than 1 mm wide and all involute for subsp. angustifolia, up to 4 mm wide and flat or involute for subsp. pratensis. Also, keep in mind there are hybrids plus cultivars in the nursery trade which can add more variables to the mix.

It is most likely to be confused with Canada Bluegrass (Poa compressa), which has a distinctly compressed stem, stem leaves are more spreading and twisted, and the callus hairs on florets are short and sparse. Fowl Bluegrass (Poa palustris) is a native wetland species that is somewhat similar, but has a longer ligule up to 6 mm long, a larger, more open and wispy panicle that emerges weeks later than Poa pratensis, and callus hairs on the floret are shorter and more sparse.