Cyperus grayoides Mohlenbr.

Illinois Flatsedge


CC = 9
CW = 5
MOC = 5

© SRTurner

Family - Cyperaceae

Habit - Perennial sedge with short, knotty rhizomes, lacking tubers, but the stem bases somewhat thickened and hard.

Stems - Aerial stems 10-60 cm long, bluntly trigonous, smooth.

Leaves - Leaf blades 10-35 cm long, 2-4 mm wide, grasslike, shorter than the stems.

Inflorescences - Irregular umbels with 1-2 sessile spikes and 3-7 long-stalked headlike spikes, the rays smooth. Inflorescence bracts 3-7, mostly longer than the rays, spreading to somewhat ascending.

Cyperus_grayoides_inflorescence.jpg Inflorescence.

© SRTurner

Spikes - Spikes 10-25 mm long, with 5-40 spikelets, hemispherical to globose, the spikelets ascending to reflexed, radiating in several planes and not clearly alternate, but the spikelet bases usually readily visible.

Cyperus_grayoides_spike1.jpg Sessile spike.

© SRTurner

Cyperus_grayoides_spike2.jpg Stalked spike.

© SRTurner

Spikelets - Spikelets 6-15 mm long, linear to narrowly elliptic, pointed at the tip, somewhat flattened in cross-section, with 3-12 florets, jointed to the axis of the spike and usually shed as an intact unit, but the individual scales sometimes also shed. Spikelet scales 2.5-3.0 mm long, barely overlapping the adjacent scales on the same side of the axis and usually somewhat spreading at maturity, ovate to broadly elliptic, bluntly angled along the back, rounded to bluntly pointed, sometimes minutely notched at the tip, the midrib often extended past the body of the scale as a short point, straight to slightly incurved, with 7-13 nerves, straw-colored to light brown, usually tinged or streaked with reddish purple, the midrib green. Stamens 3, the anthers 1.0-1.2 mm long. Stigmas 3.

Cyperus_grayoides_spikelets.jpg Spikelets.

© SRTurner

Fruits - Achenes 2.0-2.4 mm long, elliptic in outline, sharply 3-angled in cross-section, the sides flat, the surface finely pebbled, brown to dark brown or nearly black, shiny.

Flowering - July - September.

Habitat - Sand prairies, fallow fields, disturbed areas, always in dry, sandy soils.

Origin - Native to the U.S.

Lookalikes - Many other species of Cyperus.

Other info. - This sedge is uncommon in Missouri, mostly restricted to the sand prairies of the southeastern region of the state. It is uncommon beyond Missouri as well, found only in relatively small portions of four other states. Where present, it can be quite abundant. As a group, Cyperus can be challenging to identify to species. This one is characterized by having smooth rays and flattened spikelets, and by other morphological details of the spikelets and scales. The plant is rhizomatous and non-clumping. Its dry, sandy biological niche is unsuited to most other plants, translating to less competition for existing resources.

Photographs taken at Sand Prairie Conservation Area, Scott County, MO, 9-7-2020 (SRTurner).