Straw-Colored Flatsedge
Cyperus strigosus
Cyperaceae (Sedge family)

Description: This perennial flatsedge is –3' tall and unbranched. The culm is 3-angled, glabrous, and rather stout. A few leaves develop along the lower half of the culm; their blades are 4-18"' long and 2-10 mm. across, medium green, and glabrous. There is a deep furrow along the central midrib of most leaf blades. The lower leaves often wither away before flowering occurs. The inflorescence consists of an umbel or compound umbel of floral spikes; a typical umbel spans 2-5" across. A typical inflorescence consists of 1-2 sessile spikes and 3-5 spikes on stiff peduncles (or rays) up to 4" long. Some of these spikes may have 1-2 lateral spikes projecting from each of their bases; these lateral spikes are shorter. At the base of the inflorescence, there are 3-8 leafy bracts that are as long as the leaf blades and very similar in appearance. These bracts ascend slightly upward at the base and are widely spreading; some of these bracts extend beyond the inflorescence. The floral spikes are about –2" long and short-cylindrical in shape; they consist of 30-80 linear-flattened spikelets that extend more or less perpendicularly from the central rachises of the spikes in all directions. This provides each spike with a bottle-brush appearance.

Each greenish yellow spikelet is about 12-20 mm. (–") in length and 1-2 mm. across, consisting of about 5-11 florets and their scales. The florets and their scales are arranged in 2 overlapping ranks along the length of each spikelet; they become less green and more straw-colored or light brown with maturity. Each scale is glabrous, lanceolate with a pointed tip, and sharply curved (with a keel) along the middle of its length, where a green midvein occurs. The length of each scale is 3-6 mm. Each floret has an ovary, a tripartite style, and 3 stamens. The blooming period occurs during the summer or autumn. The florets are cross-pollinated by the wind. Afterwards, the florets are replaced by oblongoid achenes that are 1.5–2.0 mm. in length and bluntly 3-angled; there is one achene per floret. The root system consists of a corm-like swelling at the base of the plant, shallow fibrous roots, and spreading rhizomes. Clonal colonies of plants can develop from the rhizomes.

Cultivation: The preference is full sun and moist to wet conditions. This flatsedge readily adapts to soil that is muddy, sandy, or gravelly. The size of this flatsedge is highly variable, depending on the fertility of the soil and the age of individual plants. Because of its heat- and drought-resistant C4 metabolism, most growth and development occur during the summer.

Range & Habitat: Straw-colored Flatsedge has been found in every county of Illinois, where it is native and common (see Distribution Map). Habitats include low areas along ponds and rivers, sloughs and prairie swales, seeps, sedge meadows, ditches along roads and railroads, fallow fields, and poorly maintained gardens. These habitats can be either sandy or non-sandy. Straw-colored Flatsedge prefers sunny seasonal wetlands with a history of disturbance, although it is also found in higher quality wetlands. Sometimes it becomes a weed in fields and gardens.

Faunal Associations: Larvae of the Flatsedge Borer Moth (Diploschizia impigritella) bore into the stems and leaf bases of flatsedges (Cyperus spp.). Other insect feeders include larvae of the Sedge Gall Midge (Planetella caudata), the Yellow Sugar Cane Aphid (Sipha flava), the Viburnum-Sedge Aphid (Ceruraphis eriophori), and the Blissid bug, Ischnodemus rufipes. The value of Straw-colored Flatsedge to vertebrate wildlife is less than Yellow Nut Sedge (Cyperus esculentus) because its root system lacks tubers. However, such wetland birds as the Green-winged Teal, Blue-winged Teal, Northern Pintail, Northern Shoveler, Canada Goose, Redwing Blackbird, and Bobolink eat the seeds or seedheads of this and other flatsedges; the Canada Goose also eats the foliage. Cattle are able to browse on the foliage of flatsedges without ill effects, but it is not regarded as high quality forage.

Photographic Location: A drainage ditch in Urbana, Illinois.

Comments: This is one of the larger flatsedges (Cyperus spp.) in Illinois; it is rather variable across its range. Individual plants of Straw-colored Flatsedge (Cyperus strigosus) can become 3' tall, but this is unusual. More typically, individual plants are –2' tall. The floral spikelets of Straw-colored Flatsedge are green to yellowish green when they are immature. In contrast, the common Yellow Nut Sedge (Cyperus esculentus) has immature spikelets that are pale yellow to golden yellow. The floral scales of Straw-colored Flatsedge are unusually long and slender (easily exceeding 3.5 mm. in length) and they are relatively few in number (about 5-11) per spikelet. Similar flatsedges have shorter floral scales (less than 3.5 mm. in length) and they are often (but not always) more numerous per spikelet (easily exceeding 12 or more). Another common name of Cyperus strigosus is Umbrella Flatsedge.