The bush lupin (sometimes bush lupine in the US) Lupinus arboreus is a widely distributed coastal member of the lupin genus. It has several other common names, some of which are mentioned below.
The bush lupin is a plant of coastal scrub and dunes. It is found on the west coasts of the United States and Canada, in north-west Europe, southern South America, New Zealand and the Falkland Islands. It is considered a potential noxious weed in Australia, and also in northern California, where it was originally planted to stabilise coastal dunes. Because it has been widely introduced, there is some uncertainty about its native range; in California it is thought to be native from Point Reyes National Seashore southwards.
Blue form of Bush Lupin in flower
The bush lupin grows as a hardy perennial bush, capable of tolerating temperatures down to -12°C and living for up to seven years. It can grow to heights of up to 1.5m (hence another of its common names, tree lupin), especially in sheltered garden situations, though typical plants are much smaller in the natural habitat. It has relatively small, greenish-grey leaves, of the characteristic lupin shape. Both yellow and blue flowering forms are known, carried on a spike up to 15cm tall. It is the yellow form, often called yellow bush lupine, that is invasive. Bush lupin has been recorded as a food plant of the larva of The Streak, a species of moth.
Like all members of the Fabaceae family, the bush lupin is an effective fixer of nitrogen in the soil. As an introduced plant, it changes the chemistry of the soil, and therefore allows other exotics to establish themselves, to the detriment of the native vegetation. It also hybridises with native species such as Lupinus littoralis (the seashore lupin ) and L. rivularis (the riverbank lupin ), further endangering the survival of those forms.
A number of other species of lupin are sometimes known as bush lupins. They include:
- Chamisso bush lupine Lupinus chamissonis
- Grape soda lupine Lupinus excubitus
- Longleaf bush lupin Lupinus longifolius
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