Sedge family (Cyperaceae)
Description: This perennial sedge is ½–2' tall and unbranched. The central stem is erect, 3-angled, and mostly covered by the sheaths of the leaves. The leaves tend to congregate toward the base of the plant. The leaf blades are up to 1½' long and 1/3" (8 mm.) across; they are light green and glabrous, spreading outward from the stem. There is a conspicuous channel along the central vein of each leaf blade, especially the larger ones. The leaf sheaths are whitish green, closed, and hairless; sometimes they become pale red toward the base of the plant. The central stem terminates in an umbel or compound umbel of floral spikes; the size and shape of the umbel is rather variable (on larger plants, it is usually several inches across). Each umbel has 1-3 sessile spikes and 6-10 non-sessile spikes on straight branches of varying length. At the base of each umbel or compound umbel of spikelets, there are several leafy bracts of varying length; the largest bract is usually longer than the inflorescence. Each floral spike is about 2-3" long, consisting of 4 ranks of spikelets along its central stalk (or rachis). The central stalk is flattened and narrowly winged. The spikelets are perpendicular to this stalk and about ½–¾" long. The spikelets are yellow to golden brown, narrowly linear, and flattened in shape; they consist of 10-30 florets and their scales. The overlapping scales are appressed or slightly spreading along the length of each spikelet; each scale is 2.0–3.0 mm. in length. Each floret has a white tripartite style and yellowish brown anthers; the tips of the styles are curly. The blooming period occurs from mid-summer to early fall. Pollination is by wind. The florets are replaced by small achenes that are 1.0–1.5 mm. long, oblongoid or oblongoid-obovoid, and flattened. The shallow root system is fibrous, rhizomatous, and tuberous. The white rhizomes have a slightly segmented appearance from the brown margins of their outer membranes; the rhizomes are connected to small globoid tubers up to ½" across. Young tubers are white, while older tubers are covered by a brown outer membrane; they are usually found within 6" of the ground surface. Vegetative colonies of plants are often produced from the tubers and their rhizomes.
Cultivation: The preference is full or partial sun, wet to mesic conditions, and a friable soil containing fertile loam, silt, or sand. This sedge can spread aggressively where the ground is bare and moist. It can inhibit the growth of other plants by depleting the soil of nitrogen. Vegetative growth occurs primarily during the warm weather of summer because of the C4 metabolism of this species. Temporary flooding is tolerated.
Range & Habitat: Yellow Nut Sedge occurs in every county of Illinois and it is quite common (see Distribution Map). This sedge is native to both North America and South America, as well as Eurasia and Africa. Habitats include prairie swales, swales in open woodlands, sedge meadows, edges of ponds, sand flats and mud flats in wetlands, gardens and lawns, poorly drained areas of fields, ditches, and waste areas. Disturbed moist areas are preferred.
Faunal Associations: The caterpillars of the moth Diploschizia impigritella bore into the stems and leaf sheaths of Yellow Nut Sedge. Its spikelets and tubers are eaten by the Canada Goose and various dabbling ducks, including the Northern Pintail, Green-Winged Teal, Blue-Winged Teal, and Mallard. The Canada Goose also feeds on the foliage of Yellow Nut Sedge. Its foliage is also edible to cattle and other mammalian herbivores, while pigs and squirrels have been known to eat the tubers.
Photographic Location: The photographs were taken of plants growing in a lawn at Urbana, Illinois, and at a flower garden in Crystal Lake Park of the same city.
Comments: Yellow Nut Sedge is quite attractive, but rather aggressive, as the small tubers can persist in the ground even when a plant is pulled out by its roots. This is the most common Cyperus sp. (Flat Sedge) in Illinois. Yellow Nut Sedge has a similar appearance to Cyperus strigosus (Straw-Colored Flat Sedge) and Cyperus erythrorhizos (Red-Rooted Flat Sedge). The root systems of the latter two species lack tubers and their rhizomes, if present, are without membranous segments as described above. The spikelets of Straw-Colored Flat Sedge have longer scales (3.5–5.0 mm. in length), while the spikelets of Red-Rooted Flat Sedge have shorter scales (1.0–1.5 mm. in length), than those of Yellow Nut Sedge. Another similar species, Cyperus odoratus (Rusty Flat Sedge), has reddish or golden brown scales that are the same length as those of Yellow Nut Sedge; however, it is a summer annual that has neither rhizomes nor tubers.