Setaria viridis (Green Foxtail)

Plant Info
Also known as: Green Bristlegrass
Genus:Setaria
Family:Poaceae (Grass)
Life cycle:annual
Origin:Eurasia
Status:
  • Weedy
Habitat:part shade, sun; average to dry disturbed soil; fields, roadsides, railroads, waste places, lawns, gardens
Fruiting season:August - October
Plant height:1 to 4 feet
Wetland Indicator Status:none
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: panicle Cluster type: spike

[photo of panicle] A single, densely packed, cylindric, spike-like panicle at the tip of the stem, depending on variety either straight to slightly nodding and 1 to 3 inches long, or straight to strongly nodding (from the tip half) and 3 to 8 inches long. Clusters of 2 to 6 spikelets (flower clusters) are densely crowded on short branches along the length of the panicle, sometimes with a short gap between the lowest branches (interrupted), or the lowest branches distinctly longer giving a lobed appearance. Spikelets are flattened on one side, oval-elliptic in outline with a blunt tip, 1.5 to 2.5 mm long, with one fertile and one sterile floret. At the base of a spikelet stalk are 1 to 3 straight bristles each 5 to 10 mm long, about 2 to 5 times as long as the spikelet. Bristles are green or purple, soft with minute, upward pointing (antrorse) barbs.

[close-up of spikelets and bristles] At the base of each spikelet is a pair of bracts (glumes) that are thin with translucent edging, elliptic to egg-shaped with a blunt tip, the lower glume 3-veined and ¼ to 1/3 as long as the spikelet, the upper glume 5 to 7-veined and as long as the spikelet or nearly so. Florets are surrounded by a pair of bracts (lemma and palea). The sterile lemma is like the upper glume and as long as or slightly longer than 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 covered in tiny pits or fine wrinkles and with a conspicuous swelling at the base. The fertile lemma is oval to egg-shaped, blunt at the tip, 1.5 to 2.5 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 but smooth and shiny on the edges.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of sheath, ligule and node] Leaves are alternate, 1½ to 12 inches long, lance-linear, flat, hairless, smooth to slightly rough. Depending on the variety, leaf width is 4 to 10 mm (to ~3/8 inch) or 10 to 25 mm (to 1 inch). The sheath is open, green, hairless except for a fringe of hairs along the edge especially near the tip. The ligule (membrane where the leaf joins the sheath) is a fringe of hairs 1 to 2 mm long. Nodes are hairless and green to purplish.

[photo of plant base] Stems are smooth, erect to ascending, the lower stem often prostrate then rising at the lower node (genticulate), but not rooting at the node. Stems are multiple and branching from the base, forming loose to dense clumps.

Fruit: Fruit type: seed without plume

[photo of maturing spikelets and mature florets] 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:

Green Foxtail is a common weedy grass of distrurbed areas throughout Minnesota, including lawns and gardens. It is rather variable with two recognized varieties, both of which are in Minnesota. Var. major is a larger plant with large robust, nodding heads that are often deep purplish colored. Its spike can have prominently lobed branches near its base. Var. viridis is a shorter plant with generally straight to slightly curved spikes, typically more green with bristles varying from longer, dense, spreading and bushy, to shorter and more sparse.

The robust forms of var. major bear a striking resemblance to Giant Foxtail (Setaria faberi), which also has thick, nodding heads. The two are often confused but can be distinguished by a combination of traits: Giant Foxtail panicles mostly nod from the lower half, where Green Foxtail mostly nods from the upper half or barely nods at all. Giant Foxtail spikelets are usually 2.5 to 3 mm long and more pointed at the tip where Green Foxtail spikelets are usually 2 to 2.5 mm and more rounded at the tip. Giant Foxtail upper glumes are up to about ¾ as long as the spikelet (consistently exposing the fertile lemma) where Green Foxtail upper glumes are mostly as long as the spikelet (more consistently hiding the fertile lemma). Giant Foxtail leaves are often softly hairy on the upper surface where Green Foxtail leaves are hairless, though may be slightly rough. Giant Foxtail roots from the lower nodes where Green Foxtail does not.

The less robust var. viridis is more similar to Yellow Foxtail (Setaria pumila), which has sparse long hairs on leaves, more numerous bristles that are typically golden yellow, spikelets about 3 mm long at maturity, and the upper glume is only about half as long as the spikelet. The cultivated form of Green Foxtail is Foxtail Millet (Setaria italica), which occasionally escapes cultivation and is similar to var. major, but its fertile florets drop off separately at maturity, leaving the glumes and sterile floret behind on the stem, where in var. major the entire spikelet drops.

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More photos

Photos by K. Chayka taken in Ramsey County. Photos courtesy Peter M. Dziuk taken in Anoka, Hennepin and Ramsey counties.

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