flowering rush image

Invasive Species of the Month: April 2012

Flowering rush (Butomus umbellatus)

Also Known As

Grassy rush, water gladiolus

General Description

Flowering rush is an aquatic perennial herb that is native to Africa, Asia, and Europe. It can form dense stands that displace native vegetation, degrade fish and wildlife habitat, and interfere with water recreation. Its distinctive flowers make it easy to identify, though not all plants flower regularly. Flowering rush reproduces by seed and fragmented rhizomes that are dispersed by water.

Growth Habit

Stems and leaves are triangular in cross-section and grow from fleshy, rhizomatous roots. Along shorelines and in shallow waters, flowering rush grows 3–5 feet tall. In deeper waters (10–20 feet deep), the entire plant may remain submerged, with limp leaves suspended under the water surface.


Leaves above the water surface grow upright and are rigid and narrow, up to 6 feet long, smooth-margined, and spirally twisted at the tips. Submerged leaves are limp and up to 10 feet long.


Umbrella-like flower clusters occur at the tops of leafless stems and consist of 20–50 white to rosy-pink flowers, each less than 1 inch wide. Flowers bloom from June through August and are only found on plants in shallow water or on dry sites.

Seeds and Fruit

Small capsules contain many long-beaked seeds.


Flowering rush can be found in riparian and wetland areas such as lakeshores, riverbanks, streams, ditches, rivers, ponds, and irrigation ditches. It thrives in slow moving water.

Additional Resources

Species Identification and Characteristics Images and Overview
Montana Weed Control Association Fact Sheet
USDA Forest Service Fact Sheet (PDF)

Management and Control Resources

Biology, Ecology, and Management of Flowering Rush: Montana State University Extension (PDF)

Past "Invasive Species of the Month" Profiles