Science Centres: Aquatic Biodiversity and Biosecurity

Gypsywort smothering raupo in a Waikato lake.

NIWA has found that gypsywort (Lycopus europaeus) is likely to be at least as invasive in Auckland as it has been in Waikato, where it forms dense patches on lake edges, displacing native rushes.

Gypsywort was first recorded in Auckland in 1982. The ARC has classified it as a ‘research organism’ under its Regional Pest Management Strategy. This means the plant has the potential to significantly affect the natural or production environments of the region, but that further research and consultation is required before designating it a pest.

The ARC asked NIWA to review gypsywort’s biology, ecology, distribution, and weed potential. The study included experiments to assess the plant’s growth and flowering under a range of climate conditions using innovative controlled temperature tanks developed by PhD student David Burnett.

Gypsywort is a perennial herb in the mint family (Lamiaceae), which grows to about 1 m tall and produces white flowers with purple markings in summer. It spreads by long stolons (horizontal runners that take root at several points to form new plants), and sets considerable amounts of water-dispersed seed.