Panicum rigidulum
redtop panic grass, redtop panicum, smooth witchgrass
35-150 cm, stout, compressed.
more or less strongly compressed or keeled, sides usually glabrous or sparsely pubescent distally;
ligules 0.3-3 mm, membranous, erose or ciliate, cilia often themselves fimbriate;
blades 8-50 cm long, 2-12 mm wide, flat or folded, both surfaces usually glabrous or scabridulous, or the adaxial surfaces sparsely pilose basally.
terminal and axillary, 9-40 cm, 1/3 – 3/4 as wide as long, usually dense; ultimate branchlets usually appressed, 1-sided, scabridulous;
pedicels 0.5-1.5 mm, usually appressed, sometimes with 1-several slender hairs at the apices.
usually 1.6-3.8 mm, usually subsessile, lanceolate, green, purple-tinged, or purple, glabrous.
2/5 – 3/4 as long as the spikelets, 3-veined, midveins keeled;
upper glumes and lower lemmas subequal or the glumes slightly longer, often spreading slightly apart at the apices, midveins keeled, usually scabridulous apically;
lower florets sterile;
lower paleas to 2/3 as long as the lower lemmas;
upper florets 1.4-2 mm long, 0.6-0.8 mm wide, 2/5 – 3/4 as long as the spikelets, occasionally stipitate, lustrous, with a tuft of minute, thickish hairs at the apices;
upper lemmas thick, stiff, clasping the upper paleas throughout their length.
=18.
Panicum rigidulum
Panicum rigidulum grows in swamps, wet woodlands, flood-plain forests, wet pine savannahs, marshy shores of rivers, ponds, and lakes, drainage ditches, and other similar wet to moist places; it is rarely found in dry sites. Its range extends from southern Canada to Mexico, Guatemala, and the Antilles.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Sheaths truncate or broadly auriculate; blade bases much narrower than the subtending sheaths | subsp. abscissum |
1. Sheaths not truncate or broadly auriculate; blade bases about as wide as the subtending sheaths. | → 2 |
2. Blades usually 5-12 mm wide, flat, mostly glabrous or scabridulous; ligules membranous, 0.3-1 mm long. | → 3 |
3. Spikelets 1.6-2.5 mm long, usually over 0.6 mm wide, green or purplish-tinged | subsp. rigidulum |
3. Spikelets 2.4-3 mm long, usually less than 0.6 mm wide, conspicuouly stipitate, usually purple | subsp. elongatum |
2. Blades usually 2-7 mm wide, often folded or involute, usually pilose adaxially, at least near the base; ligules membranous, the cilia usually fimbriate, 0.5-3 mm long. | → 4 |
4. Spikelets 2-2.7 mm long, green or purplish-stained, often obliquely set on the pedicels | subsp. pubescens |
4. Spikelets 2.6-3.8 mm long, usually purple, slender, erect on the pedicels | subsp. combsii |
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