Panicum dichotomiflorum (Fall Panic Grass)

Plant Info
Also known as: Smooth Witchgrass
Genus:Panicum
Family:Poaceae (Grass)
Life cycle:annual
Origin:native
Status:
  • Weedy
Habitat:sun; average to moist soil; roadsides, waste places, fields, shores, banks, gravel pits, open woods
Fruiting season:August - October
Plant height:1 to 6 feet
Wetland Indicator Status:GP: FAC MW: FACW NCNE: FACW
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

[photo of panicle] Erect branching cluster 3 to 16 inches long at the top of the stem, at branch tips and arising from leaf axils, the lower branches of a cluster often partially hidden in the leaf sheath. Panicle branches are up to 6 inches long, ascending to spreading, with a few to several spikelets (flower clusters) mostly appressed to one side of the branch. Spikelets are 2.2 to 3.8 mm (to ~1/6 inch) long, broadest just below the middle, green to purple, and have 2 florets but appear single-flowered. Spikelet stalks are typically shorter than the spikelet.

[close-up of panicle branch] At the base of a spikelet is a pair of bracts (glumes), the lower glume ¼ to 1/3 as long as the spikelet, rounded to pointed at the tip and 0 to 3-veined, the upper glume as long as the spikelet, 7 to 9-veined, hairless, tapering to a pointed tip. Surrounding a floret is a pair of bracts (lemma and palea), the lower lemma like the upper glume and sterile; the lower palea is insignificant. The upper lemma is fertile, shorter than the upper glume, shiny and hardened, pointed at the tip, the edges rolled around the edges of the similar palea.

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

[photo of sheath, ligule and node] Stem leaves are alternate, erect to spreading, straight to floppy, flat to somewhat wavy, 4 to 25 inches long, 3 to 25 mm (to 1 inch) wide, tapering to a pointed tip, usually hairless on both surfaces, sometimes sparsely long-hairy. Sheaths are usually hairless, sometimes sparsely long-hairy. The ligule (membrane where the leaf joins the sheath) is a fringe of hairs up to 2 mm long. Nodes are hairless.

[photo of plant base] Stems are hairless, usually freely branched, erect to ascending or more often prostrate from the base and arising at a lower node (geniculate), and few to several from the base forming clumps, and may root from the lower node in wetter soils.

Fruit: Fruit type: seed without plume

[photo of mature florets] The whole spikelet drops away when mature, leaving a naked stem behind. Grains (seeds) are enclosed within the persistent lemma and palea

Notes:

Fall Panic Grass is an annual warm season grass native to much of eastern North America, though commonly weedy, popping up on roadsides, in farm fields and other areas with disturbed soils. It even volunteered in our own garden. While it is said to reach a maximum height of about 6 feet, it is more commonly half that (or less). It is distinguished by its overall hairlessness (occasionally sparsely long-hairy); clump-forming habit, stems commonly spreading from the base and rising at the lower node (geniculate); ligule a fringe of hairs up to 2 mm long; panicle branches ascending to spreading, the lower branches often partially hidden in the sheath; spikelets 2.2 to 3.8 mm long, hairless, pointed at the tip, usually appressed to one side of the branch; lower glume ¼ to 1/3 as long as the spikelet.

There are 3 recognized subspecies of Panicum dichotomoflorum: subsp. bartowense, restricted to the Gulf Coast states from Mississippi to Florida, has sheaths covered in stiff hairs that have enlarged pimple-like bases (papillose); subsp. puritanorum, restricted to Atlantic coastal areas and the southern end of Lake Michigan, has spikelets only 1.8 to 2.2 mm long and spikelet stalks are typically more than 3 mm long; subsp. dichotomiflorum, present throughout North America including Minnesota, is as described above, lacking papillose-based hairs, spikelets 2.2 to 3.8 mm long, and spikelet stalks typically shorter than 3 mm long.

We suspect Fall Panic Grass is under-reported in the state.

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More photos

Photos by Peter M. Dziuk taken in Anoka and Houston counties and in his garden. Photo by Daniel L. Nickrent via PhytoImages.

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