River bulrush (Scirpus fluviatilis)
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River bulrush, a perennial sedge, is native to most western states. It is not considered a weed in natural settings, but can be problematic. Infestations are localized. It can be troublesome in rice fields that are not rotated with other crops. It also inhabits drainage and irrigation canals. In California, river bulrush is found in the Sacramento Valley, San Francisco Bay region, North Coast Ranges, northern Sierra Nevada, and Modoc Plateau, up to an elevation of about 4300 feet (1300 m).
River bulrush seedlings are grasslike and inconspicuous.
The mature plant is found in clumps and patches. It is generally 3 to 5 feet (90–150 cm) tall and has the characteristic triangular stem of the sedge family.
Leafless stems end in egg-shaped flower clusters below which three to five leaflike structures (bracts) extend, distinguishing it from ricefield bulrush, Scirpus mucronatus, which has only one bract.
River bulrush reproduces from dark brown swellings (tubers) that form on underground stem tips. The tubers are very hard at maturity and difficult to cut with a pocketknife.