Description: This introduced perennial grass is
1½–2½' tall, producing both basal leaves and alternate
leaves along its unbranched flowering culms. The slender culms are light green,
terete to slightly flattened, and glabrous. The alternate leaves are 2-6 mm.
across and 2-5" long; they are medium green, hairless, and ascending to widely
spreading. The tips of the leaves are hull-shaped. The basal leaves are similar
to the alternate leaves, except they are usually more long and floppy. The
basal leaves are partially evergreen, while the flowering culms and alternate
leaves die down after the grains ripen. The open sheaths are medium
green, veined, and hairless. Each culm terminates in a panicle of spikelets
about 3-6" long. The overall shape of the panicle is oblongoid-pyramidal or
narrow-pyramidal. The central axis (stalk) of the panicle, its lateral
branches, and branchlets are very slender and glabrous. Lateral branches of
varying length occur in whorls of 1-5 along the central axis; they are
ascending to widely spreading. The lateral branches divide and subdivide into
smaller branchlets that terminate in spikelets about 4-6 mm. long. Each
spikelet consists of a pair of glumes and 3-5 lemmas with florets. The glumes
are about 2.5 mm. long, narrowly ovate, membranous along their margins, and
convex along their outer sides; each glume has 1-3 fine nerves. The lemmas are
about 3.0 mm. long, narrowly ovate, membranous along their margins, and convex
along their sides; each lemma has 5 fine nerves. The mid-nerve and marginal
nerves are finely pubescent along the lower half of each lemma, while the
intermediate nerves are hairless. At the base of each lemma, there is a small
tuft of fine webby hairs. Each floret has 3 anthers and 2 plume-like stigmata.
The blooming period usually occurs from late spring to early summer and the
florets are wind-pollinated. Each fertile lemma produces a single elongated
grain about 2 mm. long. The root system is fibrous and long-rhizomatous. This
grass often forms colonies of plants from the rhizomes. There is some
variability across different strains of this grass.
Cultivation: The preference is full to partial sun,
mesic conditions, cool to warm temperatures, and fertile soil consisting of
loam or clay-loam with a slightly acid to alkaline pH. Hot dry weather during
the summer can cause this cool-season grass to die out in patches if it is not
watered.
Range & Habitat:
Kentucky Bluegrass occurs in every county of Illinois and it is quite common
(see
Distribution
Map). It was introduced from Europe as a lawn grass and pasture grass.
Habitats include lawns, parks, pastures, roadsides, degraded prairies and weedy
meadows, vacant lots, waste areas, open woodlands and savannas, limestone
glades, and gravelly seeps. This grass is usually found in areas with a history
of human-related disturbance. While it is not considered a major invader (at
least in Illinois), it is often found in some native habitats as described
above. Its capacity to recover from wildfires is poor.
Faunal Associations: Kentucky Bluegrass is an
attractive source of food to many insects. Many grasshoppers are known to feed
on the foliage (see Grasshopper Table), particularly in areas that are not
regularly mowed. The caterpillars of several butterflies and skippers also feed
on the foliage; these include Cercyonis pegala (Common Wood Nymph),
Megisto cymela (Little Wood Satyr), Amblyscirtes hegon
(Pepper-and-Salt Skipper), Ancyloxypha numitor (Least Skipper),
Hesperia leonardus (Leonard's Skipper), Hylephila phyleus (Fiery
Skipper), Poanes hobomok (Hobomok's Skipper), Polites peckius
(Peck's Skipper), and Polites themistocles (Tawny-Edged Skipper). Other
insects that feed on Kentucky Bluegrass include Leptoterna dolobratus
(Meadow Plant Bug), several stinkbugs, the aphid Rhopalomyzus poae and
other aphids, the leafhoppers Doratura stylata and Latalus sayi,
the billbugs Sphenophorus parvulus and Sphenophorus zeae, the
leaf beetles Oulema melanopus and Psylliodes cucullatus, the
larvae of the moths Cosmiotes illectella and Feltia jaculifera
(Dingy Cutworm), the larvae of Popillia japonica (Japanese Beetle) and
several Phyllophaga spp. (June Bugs), and the thrips Anaphothrips
obscura. Among vertebrate animals, the foliage of Kentucky Bluegrass is a
major food source of the Canada Goose, particularly in parks with ponds. Birds
that eat the seeds or seedheads include the Wild Turkey, Ring-Necked Pheasant,
Greater Prairie Chicken, Mourning Dove, Field Sparrow, and House Sparrow.
Kentucky Blue Grass provides preferred pasturage to horses, cattle, and other
livestock; it is also eaten by the Cottontail Rabbit and Meadow
Vole.
Photographic Location: A lawn
at the apartment complex of the webmaster in Urbana, Illinois.
Comments: This grass has been introduced everywhere
and it has become ubiquitous. It is undoubtedly the most common Poa sp.
(Bluegrass) in Illinois. Distinguishing different Bluegrass species can be
tricky; it often requires a 10x hand lens while examining the lemmas of the
spikelets. Unlike some species in this genus, Kentucky Bluegrass forms a turf
from long rhizomes. Its lemmas have 5 nerves; the central and marginal nerves
are finely pubescent on the lower half of each lemma, while the intermediate
nerves are hairless. Other Bluegrass species are pubescent along the
intermediate veins as well, or they may lack pubescent veins on their lemmas
altogether. As a group, Bluegrass species differ from many other grasses by the
small tuft of webby hair that is usually found at the base of their
lemmas.