Description: This native perennial flatsedge is ¾–3' 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 up to 1½' long and ½" across, medium green, and glabrous. There is a deep channel along the central midrib of each leaf blade. The lower leaves often wither away before flowering occurs.
The inflorescence consists of an umbel or
compound umbel of floral spikes that spans several inches 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 are longer than the
inflorescence. Each floral spike is about 1–2" long and short-cylindrical
in shape; it consists of 20-50 linear-flattened spikelets that extend
perpendicularly from its central axis in all directions. This provides each
spike with a bottlebrush appearance. Each greenish yellow spikelet is about
13-18 mm. (½–¾") in length and 1-2 mm. across, consisting of
about 5-11 florets and their scales. These florets and their scales are
arranged in 2 ranks along the length of each spikelet; they become less green
and more straw-colored with maturity. Each scale is linear-lanceolate with a
pointed tip and it is curved along the middle of its length, where a green
midvein occurs; the length of each scale is 3.5–6 mm. Each floret has an
ovary, 3 stigmas, and 3 anthers. The blooming period occurs during the summer
or early fall. Pollination is by wind. Each floret is replaced by an oblongoid
achene that is 1.2–2.0 mm. long and bluntly 3-angled. The root system
consists of a corm-like swelling at the base of the plant, shallow fibrous
roots, and spreading rhizomes. Vegetative colonies 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.
Range & Habitat: Straw-Colored Flatsedge has
been found in every county of Illinois and is common. Habitats include low
areas along ponds and rivers, sloughs and prairie swales, seeps, sedge meadows,
ditches along roads and railroads, fallow fields, and gardens. 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: The caterpillars of the moth Glyphipterix
impigritella bore into the stems and leaf bases of Cyperus spp.
(Flatsedges). The value of Straw-Colored Flatsedge to vertebrate wildlife
is less than Cyperus esculentus (Yellow Nut Sedge) because its root
system lacks tubers. However, Green-Winged Teal, Canada Geese, Redwing
Blackbirds, and Bobolinks eat the seeds or seedheads of this and other
flatsedges; the geese also eat the foliage. Cattle eat 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 Cyperus
spp. (Flatsedges) in Illinois. Individual plants of Straw-Colored Flatsedge
can become 3' in length or more, but this is unusual. More typically,
individual plants are ¾–2' tall. The floral spikelets of
Straw-Colored Flatsedge are green to yellowish green when they are immature (as
revealed in the photograph above). In contrast, Cyperus esculentus
(Yellow Nut Sedge) has immature spikelets that are pale 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). Straw-Colored Flatsedge is rather variable
across its range, and some robust specimens may have measurements that exceed
what has been described above. Another common name for this species is Umbrella
Flatsedge.