Help us find the local invader, great willowherb

When you’re out and about exploring your local wetlands, lakes and rivers this summer, keep your eyes peeled for the local invasive plant, great willowherb (Epilobium hirsutum). 

Great willowherb goes incognito for much of the year but from December through to April it grows distinctive pink flowers with a white centre making it easier to identify:

• flower petals have a notch on the edge and are 2–3 cm in diameter
• leaves are slightly hairy with a ragged edge attached directly to the stem.

An aggressive invader, great willowherb can reach up to 2cm tall and can rapidly form dense infestations that outcompete native species.

Great willowherb spreads mainly by seed, easily dispersed by the wind or on clothing, footwear, vehicles, machinery and gravel.

It can also spread by broken fragments of the rhizomes (underground roots/stems) if the area is disturbed, or the plant is damaged.

It prefers wet or damp environments and can easily thrive in wetlands, lakesides, riversides and roadside ditches.

Great willowherb is currently only found in Waitaha/Canterbury. Our team has undertaken search and control around the known sites but there are still many areas where this invasive plant could be hiding.

Report great willowherb

We need your help to find any additional plants to help us understand the spread of great willowherb across the region.

Great willowherb is related to, and often mistaken for, slender willowherb (Epilobium ciliatum), and the critically threatened native herb hairy willowherb (Epilobium hirtigerum).

If you think you have found great willowherb, don’t attempt to remove it. Instead take a picture, report any sightings via our online form or call us on 0800 324 636.