Scientists' interactions with lupine (Luninus spp.) have been almost comically confused. First, they named the plant after the Latin word for wolf, lupus, on the foolish misconception that the perennials wolfed down the nitrogen in the soil. More recently, they introduced bush lupine to stabilize the California dunes only to declare it invasive a few years later. Through it all, bush lupine continues to bloom happily, offering its blue or yellow blossoms throughout the springtime.
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Yellow Bush Lupine
Common names of a plant vary among communities and no one is consistently called blue bush lupine. Various types of bush lupine offer blue flowers, including one occasionally labeled blue bush lupine but more often termed yellow bush lupine (Lupinus arboreus). Yellow bush lupine is a California native and, despite its name, can produce blue-purple flowers in U.S. Department of Agriculture plant hardiness zones 7a through 10b. Rather than devouring soil nitrogen, yellow bush lupine can set nitrogen in the soil, one reason it was introduced to California beaches. It blooms in springtime and the flowers persist into early summer.
If bush lupine does not grow as fast as a speeding bullet, it comes close. This very fast-growing perennial, left to its own devices, forms a rounded bush or small tree up to 6 feet tall in its first year of growth. The slender branches fill with gray-green leaves covered in fine white hair. Five to 12 leaflets grow together in a palmate pattern. The flower stems appear just above the leaves, bearing blue or yellow blossoms in the spring.
Flowers and Fruit
The flowers of the yellow bush lupine, whether blue or yellow, grow on long, spiky racemes. They are small and fragrant, looking something like pea flowers. After the blooms fade in summer, the plants bear fruit: brown pods laden with large, virtually indestructible seeds. The seeds last a long time and, once the species is introduced, form a persistent seed bank that makes an established colony difficult to eradicate. Seeds are spread easily by wind and rodents, increasing the range of the plant.
Over time, bush lupine changes the soil of its location. It is a nitrogen-fixing shrub and, once introduced, can spread rapidly as it did over the dune mat of the northern California sand dunes. In time, the presence of bush lupine raises the nitrogen levels of the earth it grows in to the point that the land in easily invaded by other species that would not have been able to grow there otherwise. Even if the bush lupine are removed, the plant community is forever changed.