Cyperus eragrostis Lam.
Rhizome short, thick, woody. Stems 25-90 cm high, stout, obtusely trigonous, smooth, leafy and ± thickened at base. Leaves usually < stems, 4-8 mm wide, flat, margins finely serrate; sheaths dark purple-brown. Involucral bracts 5-8, leaf like, unequal, often very much > inflorescence. Inflorescence a compound umbel, rather variable in size; rays 5-7- (9), of unequal length, each with a dense pale green to yellow-green globose or hemispherical spike at tip, 1-2 cm diam. Spikelets many, densely crowded, much compressed, ± 5-12 ×3 mm, ovoid-oblong, subacute. Glumes many, ± 2 mm long, densely imbricate, ovate, membranous, cells very distinct, whitish-cream to light brown, 1-distinct lateral nerve on each side, keel green, tip slightly recurved. Stamen 1. Style-branches 3. Nut ± ½ length of glume, trigonous, obovoid brown.
N. common throughout. S. Nelson - scattered; Marlborough - Crail Bay; Canterbury - Christchurch and environs, Ashburton, Waimate; Fiordland - Doubtful Sound. In wet ground. (N. and S. America)
First record: Buchanan 1871: 210, as "C. gracilis non R. Br."
First collection: Mangonui, T. F. Cheeseman, Dec. 1872 (AK 97322).
Formerly known in N.Z. as C. vegetus Willd.; C. gracilis J. Buch. T.N.Z.I. 3, 1871, 210 non R. Br. (Type:WELT 21287, Hutt Swamp, Wellington, labelled in Buchanan' s hand and determined as "Cyperus buchananii Kirk"); C. buchananii Kirk T.N.Z.I. 10, 1878, app. xli (based on C. gracilis J. Buch.).
C. eragrostis is most likely to be confused with C. congestus, but is distinguished by the light green to yellow-green leaves, shorter oblong spikelets, and usually open, light green, never echinate inflorescences.
C. eragrostis is a widely distributed, often locally common weed of damp waste places on margins of swamps, rivers, streams and lakes, in seepages and drains; it sometimes forms linear colonies along road drainage channels and occurs infrequently swampy places in pasture where it is sometimes closely grazed by cattle.
It is occasionally cultivated as an ornamental and has been sold in error in the trade as papyrus, but it is nuisance in domestic gardens because it seeds so freely.
