Description: This native sedge is 1–2¼' tall, consisting of an unbranched culm with 1-4 leaves along the lower-third of its length; by the time that the inflorescence of the culm develops, the older leaves are often withered. Basal sheaths of these withered leaves often persist at the base of the culm; they are brown to black. Each culm is green, glabrous, and triangular in cross-section (becoming more terete near the bottom); it is rough underneath the inflorescence, otherwise its texture is smooth. The narrow leaf blades are up to 8" long and about 2 mm. across; they are ascending to slightly recurved, green, hairless, and somewhat stiff. The sheaths of younger leaves are light green to green, hairless, and slightly concave at the mouth.
A culm usually terminates with an
inflorescence about ½–1½" long and less than ¼" (6
mm.) across. This inflorescence is stiff and erect, consisting of about 6-14
short spikelets that are appressed or ascending along the central axis (or
rachilla). These spikelets are adjacent or slightly separated from each other;
they tend to be more crowded toward the top. Young spikelets are a mixture of
green and brown, but they later become brownish black. A spikelet can have male
florets above and female florets below, all male florets, or all female
florets; this varies with the local population. Each spikelet with female
florets typically has 4-10 perigynia that are crowded together. Each perigynium
is 2.0–3.5 mm. long and 1.0–1.5 mm. across; it is brownish black,
plano-convex, ovoid with a slender beak, rounded at the bottom, and flattened.
The outer surface of the perigynium has a few longitudinal veins, while the
inner surface is without veins. The pistillate scale is ovate and equal to, or
larger than, its perigynium; it has a greenish brown central vein, otherwise it
is membranous
(clear to light brown). This scale has a slender tip. The blooming period
occurs from late spring to mid-summer. The achenes are ovoid, flattened, and
about 1.2–2.0 mm. long. The root system is fibrous and rhizomatous. This
sedge is not densely tufted at the base. Instead, individual culms are produced
from the long rhizomes. As a result, a dense mat of plants is produced. The
culms of such colonies are normally erect, although they can lean over to one
side in response to flood waters.
Cultivation: This sedge is typically found in full
sun and soil that is wet and mucky to dry and barren. It also tolerates salty
and/or highly alkaline conditions to a greater extent than many other
plants.
Range & Habitat:
Expressway Sedge is native to a few counties in northern Illinois, where it was
originally quite rare. However, in recent years this sedge has become more
abundant because of the application of road salt. As a result, the range of
this species has expanded eastward and southward in the United States. Habitats
include wet to dry prairies, prairie swales, areas along railroads, roadside
ditches, and low areas in the median strips of highways. In California, this
species has been used experimentally as a substitute for conventional turf
grass. In Illinois, this sedge is usually found in wet prairies and low areas
along roads.
Faunal Associations:
The caterpillars of several butterflies, skippers, and moths feed on the
foliage of Carex spp. (Sedges); see the
Lepidoptera Table for a
listing of these species. Grasshoppers that feed on sedges include
Stethophyma lineata (Striped Sedge Grasshopper) and Stethophyma
celata (Otte's Sedge Grasshopper). Leaf beetles that feed on sedges include
Donacia porosicollis, Poecilocera harrisii, and several
Plateumaris spp. The seeds and seedheads of sedges are an important
source of food among various upland gamebirds, granivorous songbirds, and
waterfowl (see Bird Table).
Sedges are eaten to a limited extent by mammalian herbivores, but they are not
a preferred food source. When Expressway Sedge and other sedges form dense
colonies, this provides cover for many small animals and
invertebrates.
Photographic Location: A drainage ditch along a highway in Savoy, Illinois.
Comments: This odd sedge looks like a species of grass, but isn't. After the seedheads disarticulate from the culms, it even resembles one of the Eleocharis spp. (Spike Rushes), forming the same dense mats of plants in wetland areas. However, this species has the same reproductive structures as other Carex spp. (Sedges), including the perigynia and pistillate scales of the female florets. Expressway Sedge has only a few narrow leaves (3 mm. across or less) and its inflorescence is rather small (up to 1½" long and 5 mm. across or less). The perigynia become blackish brown during an early stage of development when those of other sedges are still green or yellow, and they are largely covered by the pistillate scales. Because of these characteristics, Expressway Sedge resembles few other sedges. One of them, Carex sartwellii (Sartwell's Sedge), is a taller plant with wider leaves (up to 5 mm. across) and a larger inflorescence (up to 2½" long and 6 mm. across or more). It produces more vegetative shoots than Expressway Sedge.