Purple Loosestrife is a highly invasive perennial herb that outcompetes native vegetation, disrupts water flow, and can degrade habitats for wildlife, particularly wetland birds.

The plant can block access to waterways, impact irrigation systems, and reduce the quality of hay and pasture due to its unpalatable nature. Purple Loosestrife is a prolific seed producer, with each plant capable of producing up to 2.5 million seeds annually, which can be dispersed by wind, water, and contaminated machinery, making it difficult to control once established.

Purple Loosestrife is locally established in Oamaru, with scattered populations in Tapanui and Dunedin. The plant is found in low incidence across the region, primarily in wetland and riparian habitats.

• Size: Purple loosestrife can grow up to 3 metres tall.
• Leaves: Narrow, opposite, and less than 12 centimetres long.
• Flowers/seeds: Tall, dense spikes of purple or pink flowers that bloom from December to February. A single plant can produce up to 2.5 million small, blackish seed capsules each year.
• Root system: A thick, central taproot anchors the plant deeply in the soil with many smaller fibrous side roots spreading outward near the surface that form thick mats. These dense root systems can send up dozens of tall stems from a single base, helping the plant spread and crowd out other vegetation.
• Habitat: Thrives in wet or damp soils, often in still or slow-moving water bodies, wetlands, riverbanks, lake shores, and drainage systems.

Purple loosestrife is most visible when it flowers from December to February. 

Purple loosestrife is declared an unwanted organism in the National Pest Plant Accord (NPPA). Any species declared a pest under the NPPA cannot be sold or be in a place where plants are being sold. Pest plants cannot be propagated, bred, multiplied, communicated, released, caused to be released, or otherwise spread. 

Do not attempt to undertake control of purple loosestrife yourself. Report any sightings to Otago Regional Council.

www.orc.govt.nz/purpleloosestrife