Description: This introduced grass is a summer annual about 1-3' long. It develops several branching culms at the base; the lower branches of the culms tend to sprawl across the ground, while their upper branches are more erect. The culms are light green, terete, and glabrous, although they are mostly covered by the sheaths. The blades of the alternate leaves are up to 6" long and nearly ½" across; they are dull light green, entire or slightly curly along the margins, and often hairy toward the base. The sheaths are light green, finely ribbed, shiny or dull, and hairy.
Each upper culm terminates in 2-10
finger-like racemes up to 8" long; these racemes spread outward from a short
stalk and they are narrow and straight. The central stalk (rachis) of each
raceme is light green, flattened, and about 1 mm. across. There are many pairs
of one-flowered spikelets along the length of each raceme; they occur along
only one side of the flattened stalk. Each ovoid spikelet is light green to
brownish green, flattened, and about 3 mm. long. It consists of 2 lemmas about
3 mm. long and 2 glumes; one glume is about 1/3 to 1/2 as long as the lemmas,
while the other glume is tiny and insignificant. The lemmas enclose a single
developing grain. The blooming period occurs from mid-summer to early fall.
Each grain is ovoid and flattened like the lemmas. The root system is fibrous;
sometimes the nodes of the lower culms will form new fibrous roots. Common
Crabgrass often forms colonies.
Cultivation: The preference is full or partial sun,
moist to slightly dry conditions, and a heavy clay-loam soil. This weedy grass
can spread aggressively. Most growth occurs during the hot weather of summer
because of its C4 metabolism.
Range &
Habitat: Common Crabgrass is quite common and occurs in every county
of Illinois (see
Distribution
Map). It was introduced from Eurasia. Habitats include disturbed areas of
prairies, weedy meadows, edges of degraded wetlands, areas along roads and
railroads, lawns and gardens, vacant lots, fields, grassy paths, and
miscellaneous waste areas. This species prefers highly disturbed
areas.
Faunal
Associations: The caterpillars of Hylephila phyleus (Fiery
Skipper) and the moth Mocis texana (Texas Mocis) feed on the foliage of
Digitaria spp. (Crabgrasses). The seeds of Crabgrasses are an important
source of food to many upland gamebirds and granivorous songbirds (see
Bird Table). Crabgrass foliage
is eaten occasionally by mammalian herbivores, including the Cottontail
Rabbit.
Photographic Location: The
edge of a lawn at an apartment complex in Urbana, Illinois.
Comments: This is the most common Digitaria
sp. (Crabgrass) in Illinois. It is often found in lawns to the vexation of
many homeowners. Another introduced grass that invades lawns, Digitaria
ischaemum (Smooth Crabgrass), is a little less common. Smooth Crabgrass has
hairless sheaths and spikelets/lemmas about 2 mm. in length, while Common
Crabgrass has hairy sheaths and spikelets/lemmas about 3 mm. in length. There
are also native perennial species of Crabgrass that occur in sandy areas of
Illinois. They are more erect, have more slender leaves, and the stalks of
their finger-like racemes are terete, rather than flattened. Another common
name for Digitaria sanguinalis is Hairy
Crabgrass.