Purple nut sedge
Cyperaceae - Cyperus rotundus

What does it look like?

Nutgrass is a colony-forming perennial with a grass-like appearance that grows approximately 30cm in height. The term nut sedge or nutgrass originates from the nut-shaped roots of the plant, which are also the primary mechanism by which it spreads. Native to tropical Eurasia, it is now a weed in more than 90 countries, and has been described as one of the 'world's worst weeds' based on its distribution and effect on crops.

Leaves are linear and glossy with a prominent mid-rib, and are arranged in sets of three from a central base, growing to between 5-20cm long. Flowering stems are triangular in cross-section and produce a group of up to seven red-purple flower heads made up of narrow flattened flower spikes. The flower stalk is supported by three to six long grass-like leaves. Flowering can be erratic and may not occur after a growth period. Nutgrass produces an extensive underground network of very fibrous roots, basal bulbs, creeping stems (rhizomes) and tubers. The network branches prolifically in shallow soil, with 95% of tubers growing in the top 12cm of soil. The species rarely reproduces by seed and grows mainly from these horizontally spreading tubers.

Why is it a problem?

Nutgrass will inhabit both wet and dry areas, and almost every soil type, but will grow and reproduces more slowly in cool or waterlogged soils. Prefers farmland, coast land, riparian areas and water courses but will also tolerate drier sites such as roadsides and cropping land. Will inhabit waste areas, grasslands, forest edges and disturbed areas. Species can present a threat to agricultural areas, particularly irrigated fields.Nutgrass will compete with other plants for ground resources and is also allelopathic,with the roots releasing substances into the soil that can be harmful to other plants. It is difficult to control with any breakage of the roots resulting in further reproduction.Has been documented as having serious impacts on agriculture across the southernmost United States.The species can produce a small dry fruit with one seed, however this is rare and the seeds have low rates of viability. The primary mechanism of reproduction is by way of tuber and rhizome spread. Young plants produce white fleshy rhizomes that grow in chains horizontally in shallow soil, then grow upward and form a bulb-like tuber, which produces its own roots and new rhizomes.

It is mainly spread through human activity associated with agriculture and gardening, including vehicle movement, soil movement, ploughing, soil and crop sharing. Can be distributed with commercial root crops, seeds, and feeds.

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