Prairie Dropseed
Sporobolus heterolepis
Grass family (Poaceae)

Description: This native perennial grass forms dense tufts of sprawling leaves about 1-2' tall and 2-3' across. In each tuft, the infertile (flowerless) shoots are more abundant than the fertile (flowering) shoots. One or more flowering culms develop from the center of each leafy clump; these culms are 1–3' long and usually ascending to erect. Each culm is slender, terete, light green, and hairless. Alternate leaves are located along the lower one-fourth of each culm. The narrow leaf blades are up to 20" long and 2 mm. across; they are medium green, hairless, and either flat or somewhat rolled lengthwise. The leaf sheaths are usually hairless, although a few hairs may be present at their summits.

Each fertile culm terminates in a narrowly pyramidal panicle about 3-8" long; because of its naked branches and small spikelets, this panicle has a somewhat airy appearance. The wiry lateral branches of the panicle are 1-3" long and ascending; they subdivide into shorter branchlets that ultimately terminate in individual spikelets. The central axis of the panicle, lateral branches, and branchlets are light green to purple, slender, and hairless. Depending on their stage of development, the spikelets can be olive green, silvery gray, golden yellow, or light tan. Each spikelet is about 4-6 mm. long, consisting of a pair of unequal-sized glumes, a single lemma, a membranous palea, and a floret. One glume is 4-6 mm. long, while the other glume is 2-4 mm. long; the lemma and palea are 3.5–5.5 mm. long. Each floret has 3 reddish anthers and a pair of stigmata that are short, white, and feathery. The florets are wind-pollinated. At maturity, the florets are replaced by globoid grains that are a little less than 2 mm. across; this often causes their paleae to split into two parts. Disarticulation of the spikelets is above the glumes; the grains soon fall to the ground. The root system is fibrous and short-rhizomatous. This grass spreads primarily by reseeding itself.

Cultivation: The preference is full sun, mesic to dry conditions, and soil that is loamy, rocky, or gravelly. Because the seeds are difficult to germinate, it is easier to propagate this grass by dividing the dense tufts of leaves. Once it becomes established at a suitable site, Prairie Dropseed is long-lived.

Range & Habitat: Prairie Dropseed is occasional in the northern half of Illinois, while in the southern half of the state it is uncommon. Habitats consist primarily of hill prairies, gravel prairies, dolomite prairies, black soil prairies, cemetery prairies, prairie remnants along railroads, and limestone glades. Less often, Prairie Dropseed has been found in savannas, thinly wooded rocky bluffs, and grassy fens. This grass is found primarily in high quality natural areas. It is also cultivated as an ornamental plant.

Faunal Associations: Occasionally, the foliage is eaten by grasshoppers, including Mermiria bivitatta (Two-Striped Slantfaced Grasshopper) and Syrbula admirabilis (Handsome Grasshopper). Prairie Dropseed is the obligate host of two uncommon leafhoppers: Alflexia rubranura (Red-Tailed Leafhopper) and the recently described Memnonia panzeri. The seeds are eaten by sparrows and other granivorous songbirds from late summer into winter; these species include the Field Sparrow, Savannah Sparrow, Tree Sparrow, and Slate-Colored Junco. The foliage is readily eaten by bison, cattle, and horses. Sometimes voles and other small rodents dig burrows within the dense tufts of leaves and root mass of this prairie grass.

Photographic Location: The photographs were taken on the campus of the University Illinois and near the Anita Purves Nature Center in Urbana, Illinois.

Comments: This is one of the true prairie grasses. Because of its dense tufts of sprawling narrow leaves, there is really nothing else that closely resembles it. While some Sporobolus spp. (Dropseeds) have narrow spike-like inflorescences that are often partially hidden by their sheaths, other species in this genus have long-exerted inflorescences that are airy and open. Prairie Dropseed is a good example of this latter group; it has longer spikelets than other species in this group.

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