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Water chestnut (Trapa natans)
Photo credit: © Julia Roeser/Flickr

Flowering Rush

(Butomus umbellatus)

Report this Species!

If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.

Species at a Glance

Flowering rush is a perennial aquatic herb that can grow both as an emergent plant along shorelines and a submersed plant in lakes and rivers. It often goes unnoticed among other wetland plants until it blooms a distinctive spray of attractive flowers in late summer and early fall.


Leaves: Emergent leaves are stiff, narrow, green, and can grow up to 0.9 m (3 ft) above the water’s surface. Leaf tips may be spirally twisted. Submersed leaves are limp under water and do not flower.


Flowers: Grow in umbrella-shaped clusters on a long stalk with each flower made up of three petals, three sepals, and red anthers. Flowers are approximately 2.5 cm (1 in) across and are typically white, pink, or purple. Flowering occurs in late summer to early fall and only occurs on emergent plants.


Fruits/Seeds: Pistils ripen into dark brown fruits filled with tiny seeds.


Stems/Roots: Green stems are triangular in cross-section. The extensive root system is a thick creeping rhizome. Bulblets that form on the rhizome can easily break off when disturbed and form a new plant.

Similar Species

Leaves of flowering rush resemble another shallow water plant, bur-reed (Sparganium spp.); however, the leaves of the bur-reed are V-shaped and its female flowers appear as small spiked balls. Bur-reed grows 0.3-1.2 m (1-4 ft) tall.


Flowering rush prefers shallow and slow-moving waters but will inhabit deeper waters. It grows well in riparian zones, watercourses, and wetlands such as ditches, marshes, lakes, or streams. It cannot grow in shade and requires wet soil.


Once in a watershed, flowering rush spreads locally by underground rhizomes, root pieces, and seeds. Wildlife, water movement (water or ice), anglers, and boaters can carry this plant to new areas. Its use as a water garden plant could have also contributed to its spread over long distances.


Native to Europe and Asia, flowering rush was brought to North America as a garden plant. It is present in states along the U.S./Canadian border, extending north to the tip of Quebec and south to Illinois. In the Mid-Atlantic, flowering rush is found in New York and Pennsylvania.


Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.

Environmental Impacts

Flowering rush can crowd out native species and the large amount of underground rhizomes can harm fish and other wildlife by destroying food sources and habitats. It can also interfere with recreational activities such as swimming and boating.


Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).

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