Several plants from the UK (often introduced by settlers) are now major invasive weeds in New Zealand, including Gorse, Broom, Blackberry, and some aquatic species like New Zealand Pygmyweed (though native to NZ, it's invasive elsewhere and problematic there too) and Rhododendron ponticum, causing significant ecological and economic damage by outcompeting natives and forming dense thickets.
Common Invasive Plants (UK Origin/Introduced via UK):
Gorse (Ulex europaeus): Brought by Scottish settlers for hedging, now a widespread pest costing millions to control.
Broom (Cytisus scoparius): Another European shrub that thrives in New Zealand, forming dense stands.
Blackberry (Rubus fruticosus agg.): A vigorous bramble that invades forest edges and clearings.
Rhododendron ponticum: Can escape gardens and invade native bush, similar to its issues in the UK.
Japanese Knotweed (Fallopia japonica): A strong competitor that can form dense monocultures, affecting riparian zones.
Leyland Cypress (× Cupressocyparis leylandii): A common garden conifer that can escape and become a nuisance.
Aquatic Weeds (Some with UK Links):
New Zealand Pygmyweed (Crassula helmsii): Ironically, a plant native to NZ but introduced to the UK where it became highly invasive, eventually leading to UK bans; it's also problematic in its homeland.
Floating Pennywort (Hydrocotyle ranunculoides): An aquatic plant problematic in UK freshwaters, also listed as a significant invader in NZ.
These plants, once valued for agriculture, horticulture, or as reminders of home, found New Zealand's conditions ideal for rapid spread, creating significant costs for control and damage to biodiversity, as detailed by the Royal NZ Institute of Horticulture and Wikipedia.