Flower:

A single, densely packed, cylindric, spike-like panicle at the tip of the stem, 1½ to 3 inches long, rarely up to 6 inches. Short branches are densely crowded along the length of the panicle, each branch usually with a single spikelet (flower cluster), sometimes with a second, aborted spikelet. Spikelets are flattened on one side, egg-shaped in outline with a blunt tip, (2)3 to 3.5 mm long, with one fertile and one sterile floret. At the base of a spikelet stalk are 5 to 20 straight bristles each 3 to 12 mm long, about 1 to 3 times as long as the spikelet. Bristles are yellow to golden brown, rarely purplish, and stiff with minute, upward pointing (antrorse) barbs.

At the base of each spikelet is a pair of bracts (glumes) that are thin with translucent edging, the lower glume broadly egg-shaped with a pointed tip, 3-veined and 1/3 to 2/3 as long as the spikelet, the upper glume nearly round with a blunt to pointed tip, 5 to 7-veined and about half as long as the spikelet. Florets are surrounded by a pair of bracts (lemma and palea). The sterile lemma is like the upper glume except as long and wide as the spikelet; the sterile palea is shorter and may be visible through the translucent lemma. The fertile lemma and palea are both much thicker than the glumes, their surfaces conspicuously covered in cross-wrinkles, and with a distinct swelling at the base. The fertile lemma is oval to egg-shaped, blunt at the tip, (2)3 to 3.5 mm long, and the edges curl around the palea edges; the fertile palea is flat, as long as the lemma and with a similar texture.

Leaves and stems:

Leaves are alternate, 1½ to 12 inches long, up to 10 mm (to ~3/8 inch) wide, lance-linear, and flat though may be loosely spirally twisted. The upper surface is sparsely covered in long, white hairs near the base.

The sheath is open, green, hairless, without a fringe of hairs along the edge. The ligule (membrane where the leaf joins the sheath) is up to 1 mm long and fringed with short hairs. Nodes are hairless and green to purplish. Stems are smooth, erect to ascending, the lower stem often prostrate then rising at the lower node (geniculate), but not rooting at the node. Stems are multiple and branching from the base, forming loose to dense clumps.

Fruit:

The glumes and sterile lemma turn tan and papery as they mature, the fertile lemma and palea hardening and turning darker brown. The entire spikelet drops off when mature, leaving the bristles behind on the stem.

Notes:

Yellow Foxtail, known as Setaria glauca or Setaria lutescens in older references, is a common weedy grass of disturbed areas throughout Minnesota, including lawns and gardens. It is easily distinguished from other Foxtails by the numerous stiff, spreading yellow to tawny bristles on the panicle, upper glumes about half as long as the spikelet, and the sparse long hairs on leaves near the base. There are 2 recognized subspecies, both of which have been found in Minnesota: subsp. pumila is most common, widespread throughout the state, and generally described above; subsp. pallidefusca (formerly Setaria pallide-fusca), to-date only recorded in Anoka County, is not well documented but may have smaller spikelets (2 to 2.5 mm vs. 3 to 3.5 mm) and reddish bristles rather than golden.