The genus Lupinus contains approximately 200 species native to the Americas and the Mediterranean region; they are generally hardy in U.S. Department of Agriculture plant hardiness zones 4 to 8. Lupines are legumes with palmate leaves and attractive flowers, and they are often used as garden ornamentals. Species varieties, however, often don't fare well in the garden, and hybrid lupines (Lupinus x hybrida) have been developed for improved domestic performance.

Some of the most popular hybrid lupines, the so-called Russell hybrids, grow to between 1 and 3 feet in height and flower profusely in summer.

Flower Form

Lupine flowers form on flower stalks that may range in length from 3 to 18 inches. The flowers themselves are shaped like those of other legumes, with their lower petals forming a cup shape. Depending on the variety, the flowers may be blue, purple, pink, white, yellow or even bi-colored.

After flowering, the plant develops hairy seed pods, each of which contains three to nine seeds. The seeds are about 1/4 inch long and resemble beans.

Heat Tolerance

American lupine species are native to the western United States, where they grow primarily in cool alpine habitats, and although lupine grows well in full sun, it can benefit from shelter from the afternoon sun during the summer. It does not do well in hot, humid climates, and in USDA zones 7 to 9, it fares better when it is grown as an annual rather than as a perennial.

Weediness and Invasiveness

Some lupine species, such as bigleaf lupine (Lupinus polyphyllus), have proven to be problematic outside of the context of the garden. This species, also sometimes called garden lupine, is an ornamental perennial that is hardy in USDA zones 3 to 6. It typically grows to between 3 and 4 feet in height, and some specimens may reach 5 feet. It has hollow stems and compound leaves, each of which is made up of nine to 16 leaflets.

Bigleaf lupine is a highly adaptable plant that can tolerate a wide range of growing conditions; although it prefers cool, moist climates, it tolerates dry periods, and it is able to grow well even in nutrient-deficient soils. Because of its adaptability, it is able to spread into areas where it's not necessarily welcome. In the eastern United States, it is considered an invasive species, and it has escaped from gardens and spread widely through the Midwest, the Northeast and eastern Canada.

Lupine Toxicity

Some species of lupine, such as silky lupine (Lupinus sericeus) and velvet lupine (Lupinus leucophyllus), are considered to be toxic because of the alkaloid compounds they contain, especially in their seeds and seed pods. Silky lupine is hardy in USDA zones 3 through 9 and velvet lupine is hardy in USDA zones 8a through 10b. The toxins are particularly dangerous to livestock that may graze on the plants and their seeds. Potential effects of the toxins include lethargy, breathing difficulties, loss of muscle control, birth defects when consumed by pregnant animals, and even death if the seeds are consumed in large quantities.