What Ontario is doing

To prevent this unwanted invader from spreading in the province, Ontario has regulated flowering-rush (Butomus umbellatus) as a restricted invasive species under the Invasive Species Act.

Learn about the Invasive Species Act and regulations.

Background

Flowering-rush is a perennial aquatic plant native to Africa, Europe and Asia. It grows in shallow waters up to 3 metres in depth of lakes, rivers and wetlands. It was brought to North America intentionally as an ornamental garden plant and ballast waters from trans-Atlantic ships also may have played a role in its introduction.

This plant has become a significant concern due to its rapid spread along shorelines and in shallow areas of waterbodies, often through:

  • improperly discarded plant material
  • movement of boats
  • flooding events

Flowering-rush can spread by:

  • seed
  • rhizomes (underground stems) that send out roots in the form of bulbils (small onion-like buds), which can detach and spread in water currents
  • rhizome fragmentation
  • muskrats or waterfowl that use or disturb parts of the plant
  • ornamental use in water gardens, which can lead to accidental releases in waterbodies

Range

Flowering-rush was first discovered in Canada in 1897 along the St. Lawrence River in Quebec. Since then, it has spread across the northern United States and Canada.

Within Ontario, the plant is currently known to occur in:

  • Lake Erie
  • Lake St. Clair
  • Lake Ontario
  • the western part of the St. Lawrence River
  • many inland water bodies and wetlands in Southern Ontario

View an up-to-date distribution map of flowering-rush.

Impacts of flowering-rush

Flowering-rush forms dense stands that can displace native vegetation like willows, cattails and wild rice. Its presence in a new ecosystem can reduce overall biodiversity.

The plant can also impact recreational opportunities like boating, fishing and swimming and negatively alter habitats such as nesting sites and rearing areas for birds.

How to identify flowering-rush

Flowering-rush may occur as an emergent plant in shallow water (up to 3 metres), growing up to 1.5 metres tall. It has long, upright grass-like leaves that are triangular in cross-section that twist toward the leaf tip.

Flowering rush may also occur as a submergent plant in deep water (3 to 6 metres), with limp leaves suspended in the water column.

The plant is easily identified when flowering, with large umbrella shaped clusters of small, pale pink to rose-coloured flowers at the top of the stem. Each flower has 3 petals and 3 sepals (the sepals under the petals are also pink and look like small petals), and each plant typically produces 20 to 50 flowers. Beneath the ground, the plant has creeping underground stems that help it spread.

Similar species

Flowering-rush can be mistaken for some native aquatic plants like bulrushes. However, the plant’s unique triangular-sectioned leaves and distinctive pink umbrella shaped flower clusters set it apart from other native look-alikes.

What you need to know

  • Learn how to identify flowering-rush and prevent its introduction or spread in Ontario’s waterways.
  • It is illegal to:
    • possess or transport flowering-rush in a provincial park or conservation reserve
    • bring flowering-rush into Ontario
    • deposit, release or propagate flowering-rush, including planting it or any other actions which may encourage its spread or growth
    • buy, sell, lease or trade flowering-rush in Ontario
  • Never keep or grow flowering-rush in an aquarium, water garden or for any other purpose.
  • Always clean, drain and dry your watercraft before transporting it to another waterbody.
  • As of January 1, 2022, boaters must open or remove drain plugs and other devices to allow water to drain. They must also take reasonable measures to remove plants, animals and algae from their watercraft, watercraft equipment and trailer before transporting them overland.
  • Boaters must ensure watercraft, watercraft equipment and trailers do not have aquatic plants, animals or algae attached to them before arriving at a launch site or placing the watercraft into any waterbody.

Reporting illegal activity

If you have any information about the illegal importation, distribution or sale of flowering-rush, report it immediately to either:

If you’ve seen flowering-rush or another invasive species in the wild: