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Weed Identification

knotroot foxtail



Scientific Name

Setaria parviflora

Other Common Names:

marsh bristlegrass
knotroot bristlegrass
yellow bristlegrass

Synonyms (former Scientific Names):

Panicum geniculatum
Chaetochloa geniculata
Chaetochloa imberbis
Setaria geniculatum
Setaria gracilis


Knotroot foxtail is a warm-season perennial rhizomatous grass and mature plants can reach over 3 ft in height. It grows from late March or early April until fall from short, knotty, branching rhizomes. Foliage is a distinctive whitish green. The base of the plant is slender and wiry. It produces two and sometimes three seed crops during one growing season-the first one during May or June. Bristles are left along the seed stalk after the seeds disseminate. It grows best on moist or wet sites.


Leaf blades are 0.1 to 0.4 inches wide and 2.25 to 10 inches long. The upper side of the leaf near the stem can be hairy. Leaf sheaths are keeled and hairless. Leaves have a prominent midrib. The leaf sheath is rounded with generally shorter than average internodes and often purple tinged. The ligule is a fringe of short hair.

Identifying Characteristics

Knotroot foxtail has small hairs on the lower leaf surface. The ligule is a fringe membrane to 0.4-13.0mm. Stems are smooth. It produces short, knotty rhizomes. The rhizomatous growth contributes to the invasiveness of the species in pastures.

Flower Seed Head

The seedhead is a cylindrical panicle, similar to other foxtails, but with a more compacted size than annual species. Seedheads are purple or yellow. Each spikelet has 4-12 bristles that are 0.1 to 0.5 inches long.

Where Found

It occurs in cultivated areas, fields, pastures, lawns, turf, roadsides, railroad beds, and waste areas. It is native to the United States, Central America, and South America. It has been introduced to South and East Asia and South-west Europe. In Florida, it grows on wet sandy soils, sloughs, and acid flatwoods. In Texas and Louisiana, it grows well on salty prairie sites; also grows on salt marshes if water level is relatively low.

Leaf Hair on Upper Surface

no hairs

Leaf Arrangement

rolled in bud

Mature Leaf Width

less than 5 mm
6 to 15 mm





Life Cycle



not present



Ligule Length

1-2 mm

Plant Type