What is it?
Russell lupin, Arthur's Pass National Park
Russell lupin (Lupinus polyphyllus) is an exotic plant that can grow up to 1.5 metres. It is a perennial species, i.e. it flowers and sets seed in the summer, dies back to the stem base over winter, to re-emerge the following summer.
Russell lupins produce long, colourful flower heads. The flowers are pea-like and come in a variety of colours; blue, purple, orange, yellow, pink, white or a mixture of two colours. These flowers appear from September to February. The leaves, divided into green leaflets, are splayed out like fingers on a hand. Stout seedpods are produced that explode in the summer heat, releasing many dark brown seeds.
Why is it a problem?
Although Russell lupins are beautiful to look at, they can be an aggressive weed. Of particular concern is the invasion of Russell lupins into Canterbury's braided riverbeds, and the impacts they have on these ecosystems.
Unique birds live and breed in the braided riverbeds of Canterbury. Birds such as the vulnerable ngutu pare/wrybill and tara/black-fronted tern have adapted to nesting and feeding in unstable braided river environments. One of the world's rarest wading birds, the kakī/black stilt, feeds in shallow river braids. Russell lupins change these unstable braided river environments by forming dense stands on bare gravel areas. Their roots become entwined and hold the gravel together, forming stable areas. The river erodes the edges, forming steep banks. This restricts the water to form deep, fast-flowing channels, unsuitable for wading birds to feed in. The dense stands also take over the open spaces braided river birds like to nest in.
Canterbury's braided rivers are also home to unique native plant communities. Special plants such as the cushion forming 'forget-me-not' (Myosotis uniflora) and rare, tiny woodrush (Luzula celata) are mostly confined to riverbeds. Whole plant communities are especially adapted to growing in the challenging environment of shifting gravels, extreme temperatures and limited nutrients. This natural vegetation is often low-lying and sparse, providing ideal conditions for Russell lupins to establish themselves in. Dense stands of lupins eventually shade out and displace these special threatened plants and whole native plant communities.
Lupins are well adapted to living in the challenging environments of braided rivers. They can produce their own nutrients (nitrogen) and are very effective at dispersing their seeds. The seeds are dropped close to the parent plant, allowing the population to spread a couple of metres each year. Seeds also spread further if they are carried in waterways, allowing Russell lupins to creep down riverbeds and invade new areas.
Lupin spread is also increased by people actively dispersing seeds along roadsides and waterways, and by roadwork contractors using gravel containing seed.
Russell lupins may appear harmless and pretty growing in the garden or along roadsides, but the potential for them to escape and take over nearby waterways is enormous.
What can you do?
Listed below are some ways in which you can help halt the spread of Russell lupins into our valuable braided riverbed ecosystems and waterways:
- Refrain from buying or planting Russell lupin seed or plants.
- Avoid picking or transporting lupin seed heads between places.
- Find out more about braided rivers
- Inform others of the negative impacts Russell lupins have on our braided river ecosystems.
- Contact your local Department of Conservation office for further information.
Canterbury's braided rivers