Sporobolus compositus (Rough Dropseed)

Plant Info
Also known as: Tall Dropseed, Composite Dropseed
Genus:Sporobolus
Family:Poaceae (Grass)
Life cycle:perennial
Origin:native
Habitat:sun; average to dry sandy or gravelly soil; prairies, fields, roadsides, along railroads
Fruiting season:August - October
Plant height:24 to 50 inches
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: Cluster type: panicle Cluster type: spike

[photo of terminal panicle] Slender, erect, branching cluster up to 10 inches long at the top of the stem, partially or mostly enclosed by the leaf sheath, with smaller panicles in the upper leaf axils usually fully enclosed by their sheaths. Panicle branches are appressed with a few to several spikelets (flower clusters) per branch. Spikelets are lance-elliptic in outline, slightly flattened, 4 to 6 mm (to ¼ inch) long, light green to purplish, overlapping along a branch but not tightly crowded, and have a single floret.

[close-up of spikelet] At the base of a spikelet is a pair of bracts (glumes), both thin, hairless, awnless, 1-veined, lance to egg-shaped with a blunt or pointed tip, the lower glume 2 to 4 mm long, the upper glume 2.5 to 5 mm long often a little longer than the lower glume but distinctly shorter than the spikelet. Florets are surrounded by a pair of bracts (lemma and palea), both similar to the glumes but larger, 3.5 to 6 mm long, the lemma 1-veined, the palea 2-veined and slightly shorter to slightly longer than the lemma.

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

[photo of sheath, node and ligule] Leaves are basal and alternate, mostly on the lower stem, 6 to 20 inches long, 2 to 4 mm wide, widest at the base with long taper to thread-like tip, flat or rolled in along the edges (involute). Basal leaves are somewhat densely tufted, thin and wiry. The sheath is hairless but rough textured. The ligule (membrane where the leaf joins the sheath) is a fringe of very short hairs. Nodes are smooth.

[photo of leaf hairs] The 4 to 7 stem leaves have long, scattered hairs on the upper side, especially near base. Stems are stout, hairless, erect to ascending, sometimes tipping from the weight of the mature panicle, and multiple from the base, forming loose clumps.

Fruit: Fruit type: seed without plume

[photo of mature spikelet] Exposed spikelets turn straw-colored at maturity, enclosed spikelets often become dark gray to colorless and nearly transparent. Mature florets drop off individually leaving the glumes behind on the stalk, but they eventually drop off, too. Grains (seeds) are gray to reddish-brown, irregularly oval to oblong, 1.5 to 2mm long, somewhat flattened with a large dark brown to blackish germ on one side.

Notes:

Widely tolerant of both dry and mesic soils, Rough Dropseed ranges throughout both short and tall grass prairie regions in North America and extending into the arid SW and temperate New England to the NE. In Minnesota, both in our direct field observations and herbarium records, it does lean towards drier sites, however, there are huge holes in county records and one might assume that many more mesic sites where it was present were plowed down long before a wandering botanist showed up. While it is the most robust of all the Dropseed species, with several references noting heights of 5-6 feet, most specimens we've found have been 2-4 feet in height and in the landscape it has a somewhat obscure profile due to the panicle staying tightly contracted within the sheaths. Besides the enclosed panicles, it is otherwise identified by the single-flowered, awnless and hairless spikelets 4 to 6mm long, both glumes shorter than the spikelet, hairless sheaths, and leaves sparsely hairy at the base.

It is most similar to Sand Dropseed (Sporobulus cryptandrus), which is also perennial with its panicles (at least in part) enclosed by the sheaths. However S. cryptandrus is a much smaller statured plant with hairless leaves except for a dense tuft of long hairs on the back of the sheath opposite the ligule, its panicle is at least partially exserted from the sheath with spreading branches, and the spikelets and components thereof are roughly half the size of S. compositus. Rough Dropseed is too often overlooked in restoration plantings and I've observed it in a residential lawn where the mass of long, wiry, filamentous basal leaves all lying in the same direction create an aesthetic impression of windblown prairie.

There are 3 recognized varieties of S. compositus: var. macer, present in the south-central US, is rhizomatous rather than clump-forming; var. drummondii, also present to our south, has slender stems and upper sheaths usually less than 2.5 mm wide; var. compositus, the most common and found across much of North America, has stout stems and upper sheaths usually more than 2.6 mm wide

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More photos

Photos by K. Chayka taken in Dakota County. Photos courtesy Peter M. Dziuk taken in Big Stone and Dakota counties.

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