Flora of New Zealand Series

Nut Grass.

Rhizome wiry, far-extending, with prominent, ellipsoid, often fibrous-coated tubers. Stems 10-35 cm high, 3-angled, with many leaves at ± bulbous base. Leaves usually < stems, 2-3 mm wide double-folded, recurved at maturity, margins scabrid towards tip; sheaths dark brown. Involucral bracts 2-4, leaf like, lowest ± = inflorescence. Inflorescence usually a simple umbel with few slender rigid rays. Spikelets dark brown in digitate clusters of 3-10, linear, compressed, subacute, ± 5-15 × 1-2 mm. Rhachilla winged. Glumes ± 3 mm long, ± densely imbricate, ovate, obtuse, membranous, deep red-brown or red-purple with green keel, ± nerved. Stamens 3. Style-branches 3. Nut trigonous, obovoid, much < glume, rarely maturing.

K., N. North Auckland; Auckland - Auckland City, Bay of Plenty, Rotorua; Gisborne City; Hawkes Bay - Wairoa; Taranaki - New Plymouth; Wellington - Raetihi, Wanganui, Raumati. S. Nelson - Motueka, Nelson City. (Almost cosmopolitan in warm regions)

First record: Cheeseman 1883: 294.

First collection: Remuera. New Zealand (K). The label is undated but the sheet was annotated "rec' d 1/73" [1873] Early collection in N.Z. are also undated.

C. rotundus resembles and could be confused only with C. esculentus but differs in the wiry rhizomes with tubers at intervals along their length, leaves usually < stems, and dark red-brown, shinning glumes.

C. rotundus is one of the most widely occurring abundant and troublesome weeds of tropical and temperate regions, and the subject of the greatest number of papers in weed literature. It is difficult to control to eradicate, and research workers in many countries over a long period have covered the life history, ecology, reproduction and dispersal, and in recent years its physiology in relation to the action of a range of chemical herbicides.

Nut grass is effectively reproduced by rhizomes and tubers dispersed by diverse means. The risk of their dispersal in soil about roots of horticultural plants is recognised in N.Z. legislation; under the Noxious Weeds Act 1950 (Section 6 (3)) there is an obligation on occupiers of registered plant nurseries to keep their land free of this weed.

It is a troublesome weed in gardens, market gardens, and some cultivated land, and breaks up asphalt footpaths, margins of sealed roadways, and gutter channels in suburban sites. The plant is often a shy flowerer, especially in colder districts such as Nelson. The foliage is frost-tender but this has no noticeable effect on the underground parts.