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Tropical finger-grass, better known in the US as southern crabgrass, is one of the crabgrasses that invade lawns, gardens, and fields every summer, especially in the Southeast. It is so similar to large crabgrass that the two are usually told apart only with a hand lens. Its stems creep and root at the joints, and its seedhead splits into several slender, finger-like branches.

Appearance

Growth form
A grass, up to about 3 ft (1 m) tall in good conditions but usually much shorter, often forming low mats that root at the lower joints.
Leaves
Flat blades about 2–8 in (5–20 cm) long and 1/5–3/5 in (5–15 mm) wide, usually hairy, with hairy lower sheaths.
Flowers
The seedhead splits into about 3–8 slender, finger-like branches (some references say 2–9).
Flowering time
July to October in the Mid-South.

Look-alikes

Large crabgrassDigitaria sanguinalis

Hard to tell apart in photos. The main difference is the length of the , a tiny scale at the base of each small seed cluster, so you need a hand lens or a close-up photo of the seeds.

Why they get mixed upSame growth habit, hairy leaves, and finger-like seedheads; often grow together.

Smooth crabgrassDigitaria ischaemum

Smooth crabgrass has few or no hairs, usually only where the blade meets the sheath. Southern crabgrass has leaf sheaths densely covered in stiff hairs.

Why they get mixed upAnother common summer lawn crabgrass with similar seedheads.

Where it lives

Typical habitats
  • Lawns
  • Gardens
  • Crop fields
  • Roadsides
  • Pastures
Range
Most common in the Southeast, east of the Appalachians and through Florida, west to Texas and north into Kansas and Nebraska; along the coastal plain it reaches as far north as Connecticut. It also grows in the West Indies and Mexico through South America.
Preferred conditions
Forms dense stands in open, disturbed, or thin-turf spots.
Flowering

Flowers Jul–Oct

Flowers Jul–Oct

Life cycle

Reproduction
Reproduces by seed. Seeds rarely travel far on their own; mowing and hay can carry them long distances.

Name and classification

About the name
Some references treat it as a variety of large crabgrass (Digitaria sanguinalis var. ciliaris). Some US references count it as native, while others think it came from the Old World, probably Asia.

Conservation

IUCN Red List
NENot EvaluatedNot yet assessed

Culture and stories

Culture and stories
  • Despite its weedy reputation, this species is a nutritious warm-season grass that has been used as livestock forage, and a forage cultivar called 'Red River' crabgrass exists.

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Tropical Finger-grass (Digitaria ciliaris) — identification, habitat & look-alikes | Moeyo