Description

General: Purple nutsedge is a colonial, herbaceous, perennial with fibrous roots that typically grows from 7-40 cm tall and reproduces extensively by rhizomes and tubers. The rhizomes are initially white and fleshy with scaly leaves and then become fibrous, wiry, and very dark brown with age. Rhizomes may grow in any direction in the soil. Those growing upward and reaching the soil surface become enlarged forming a structure 2-25 mm in diameter variously called a “basal bulb, a tuberous bulb, or a corm” that produces shoots, roots, and other rhizomes. Rhizomes that grow downward or horizontally form individual tubers or chains of tubers. Individual tubers are dark reddish-brown when mature, about 12 mm thick, and vary from 10-35 mm long.

The dark green, shiny, three-ranked leaf blades arise from or near the base of the plant. They are narrow and grass-like ranging in size from 5-12 mm wide to 50 cm long and have a prominent channel in cross section. The leaf sheaths are tubular and membranous and attach to compact nodes at or near the base of the plant.

The upright culms or stems are 10-50 cm tall, smooth, triangular in cross section, and support a much-branched inflorescence. Two to four leaf-like bracts subtend the inflorescence which is umbel-like consisting of 3-9 unequal length branches (sometimes referred to as rays) bearing spikes of 3-10 spikelets. Spikelets are flattened and linear ranging in length from 10-30 mm long, and generally dark reddish purple or reddish brown in color. Each of the 20 or so flowers (florets) in a spikelet are each subtended by a keeled scale (glumes) 2-5 mm long that have a green midvein and a membranous margin. The flowers are bisexual each with three stamens and a pistil bearing three stigmas. Fruit, although rarely produced, consists of a three-angled achene (nutlet).

Purple nutsedge possesses the C₄ photosynthetic apparatus, which is an adaptation to assimilating CO₂ at higher temperatures and higher light intensities compared to C₃ pathway plants. C₄ plants typically exhibit their best growth rates at temperatures characteristic of tropical and subtropical regions. The leaf anatomy for purple nutsedge is of the Krantz-type. Sheaths of cells that form around the vascular bundles serve to compartmentalize the photosynthetic events. Greater anatomical and physiological details for purple nut sedge are given by Wills (1987).

Cyperus esculentus, yellow nut sedge, is another problematic weedy species that reproduces by tubers. It is more widespread and also grows in more temperate parts of the United States. Purple nutsedge is readily distinguished from yellow nut sedge and other sedges by its purplish brown spikelets and scaly or wiry rhizomes that often bear chains of tubers.

Distribution: Purple nutsedge is reportedly native to India, but it has been introduced around the World (Holm et al. 1977). The plant is a serious pest in the Southeast ranging from Virginia to central Texas. It also has become established in parts of Arizona and California and has the potential to invade other Pacific states. (Southern Weed Science Society 1995; FICMNEW 1997). This species occasionally occurs in more temperate regions. For example, its presence in Stearns County, Minnesota was documented by a specimen in the University Herbarium collected by J. E. Campbell, July, 1896 (MIN: accession number 81217), but purple nutsedge has not persisted there and other cold locales. The northern limit of nutsedge in Japan is in a region where the average minimum atmospheric temperature is -5⁰C, the temperature below which tubers will not germinate (Ueki, 1969). Temperature appears to limit the species to more tropical and warm temperate regions. For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site.