http://articles.extension.org/pages/65213/purple-nutsedge-cyperus-rotundus-in-greater-depth

Purple nutsedge (Cyperus rotundus) is a colony-forming perennial weed that seriously impacts agriculture across the southernmost United States. Native to tropical Eurasia, purple nutsedge has become a major weed of vegetable, row, and plantation crops in tropical and warm temperate climates around the world, is very difficult to manage with either organic or conventional weed control strategies (William, 1976; Bangarwa et al., 2008; Wang et al., 2008), and has been called the world's worst weed (Holm et al., 1991). Purple nutsedge is one of the most extensively researched non-cultivated plant species on the planet, yet the complexities of its life cycle, and its multiple adaptations to environmental extremes and weed control tactics are as yet incompletely understood.

Purple nutsedge is a grass-like weed in the sedge family (Cyperaceae) with top growth 4–30 inches tall (Fig. 1), an extensive underground network of basal bulbs, fibrous roots, thin wiry rhizomes (Fig. 2), and tubers borne in chains of 2–6 or more on rhizomes, with tubers spaced 2-10 inches apart. The leaves are mostly basal, dark green, 0.1–0.25 inches wide with a prominent midrib, and abruptly tapered at the tips. The purplish to red-brown inflorescence (Fig. 1) is borne on a culm (stem) that is triangular in cross section and usually taller than the foliage (Bryson and DeFelice, 2009). The inflorescence itself consists of an umbel of spikes, some of which are sessile, and others are borne on stalks of unequal length.The subtending leaflike bracts are usually shorter than the longest spikes.