Cyperus iria aka Umbrella Sedge

Cyperus iria is also called ricefield flatsedge. It belongs to Cyperaceae, the sedge family. It is native to tropical and subtropical parts of the Old World. These include Africa, Asia, New Guinea, and Australia. It now grows wild in many other regions. It grows in rice fields, marshes, ditches, and along river banks. United States records reach as far north as Maine.

This grass-like plant grows in coarse, upright clumps. It is an annual, though some plants live longer. Reported heights range from 0.26 to 2.6 feet [0.08–0.8 metres]. Its roots form a short mass of yellow-red fibres. The green stems, called culms, are solid and smooth. A cut across a culm shows a near-triangle shape. The narrow, hairless leaves grow in turn along the stems. Each leaf blade has a V-shaped fold and glossy surface. Small bumps make the leaf edges and midrib feel rough. Sheaths wrap around the stem base. They may have reddish-brown tones.

The loose flower heads branch to form compound umbels. These have smaller groups of flowers on their branches. Four to seven leaf-like bracts sit below the heads. The long spikes range from yellow-green to golden-brown. Two glumes, or small scales, enclose each small flower. In the United States, it blooms in summer and fall. In its native conditions, it may bloom all year. The fruit is a glossy brown achene with three sides. Its shape is like an egg, wider toward the tip.

This fast-growing sedge does well in full sun and moist ground. It grows in clay, loam, or sand with acid to neutral pH. It copes with wet soil, brief floods, and some dry spells. NC State lists USDA hardiness zones 4–9. Its strong urge to spread is the main concern in gardens. One plant can yield 3,000–5,000 seeds. A second generation can grow within the same season. Pull plants before they flower to help curb seed yield. It is a serious weed in rice, cotton, and soybean crops.

The plant hosts many insects, as well as their young larvae. People weave mats from its leaves and culms. Traditional medicine uses it for rheumatism and menstrual disorders. These reports do not prove that it has medical benefits. The supplied sources do not record food use for this species. Useful Tropical Plants reports no known hazards. This does not prove that the plant is safe. The same source gives its IUCN status as Least Concern.