rough dropseed (composite dropseed, tall dropseed)
Sporobolus compositus (Poirot) Merr.

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Rough dropseed is widespread in the eastern two-thirds of the United States, where it grows along roadsides and other at least partially disturbed sites as well as in a variety of habitats including prairies and woodlands. This species is widespread in Iowa, but it most often occurs on dry prairie slopes and gravelly hills. Like hidden dropseed (Sporobolus clandestinus), the flowering heads of rough dropseed are usually partially concealed within the sheath of the leaf immediately below it. Rough dropseed is most similar to hidden dropseed, but can be easily distinguished by its usually smooth leaf sheaths, much longer flowering heads, shorter spikelets, smooth lemmas, and paleas equaling the lemmas. Rough dropseed can be seen in flower from August through October in Iowa.

Much of the literature on prairies and grasses, including Pohl’s 1966 Grasses of Iowa, has this species listed as Sporobolus asper, the Latin name by which it is most widely known. Recent work for a treatment of Sporobolus for the Flora of North America revealed, however, that the correct name for this species is actually S. compositus.

Etymology: Sporobolus from the Greek sporo = seed and ballein = to throw, referring to the free seeds in many species of this genus that are sometimes forcibly ejected when the usually mucilaginous fruit wall dries; compositus from the Latin for compound, perhaps referring to the large flowering heads with many appressed branches.


Plants perennial, tufted, usually not rhizomatous. Culms 45-130 cm tall. Leaves with the sheaths open, usually smooth, lacking a conspicuous tuft of hairs at the summit; ligules 0.1-0.5 mm long, a line of hairs; blades 5-40 (-60) cm long, 2-4 mm wide, flat to rolled, the lower surface usually smooth, the upper surface smooth or hairy, often with hairs present toward the base. Flowering heads terminal and axillary, 5-26 cm long, 0.5-1.5 cm wide, contracted, partially or sometimes completely enclosed by the subtending leaf sheath; primary branches appressed to the main axis. Spikelets 4.5-5.4 mm long, straw-colored to purple-tinged, laterally compressed, lacking any awns; glumes unequal, glabrous, membranous, usually 1-nerved, lower glumes 2.6-3.5 mm long, upper glumes 3.2-4.8 mm long, at least 2/3 the length of the florets; lemmas 4.4-5.2 mm long, smooth, 1-nerved, membranous, acute; paleas 3.9-4.9 mm long, obtuse, equaling the lemma, 2-nerved, membranous. Fruits xxx mm long, ellipsoid. Chromosome number 2n = 72.


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