There are over 80 species of lupines (Lupinus) in California. Although it is not an infallible tool for identification, lupines in sagebrush and alpine areas where water is scarce are often dramatically silvered in soft, downy hairs, a environmental response for conserving water. The satiny sheen reflects some of the sun’s radiant energy while preventing evaporation from the leaf surfaces.
Silverleaf lupine (L obtusilobus) is a perennial growing in gravelly, open places up to 11,400 feet. It is native to and found in Northern California and far western Nevada.
The leaves of silverleaf lupine are palmate with 6 or 7 leaflets. The leaves, as well as the stem, which grows from a woody base, are covered in silky, silvery hairs pressed against the surface. A pair of stipules (leaflike structures) occur at the base of the leaf petioles (stalks). There is a joint-like swelling (pulvinus) at the base of the petiole which allows the leaves to open or close in response to changes in intracellular water content.
The silverleaf lupine inflorescence is a raceme – unbranched and pedicelled (stalked) flowers arranged along a central axis with the oldest blooms at the base and newer blooms near the top. As a member of the Pea Family (Fabaceae), silverleaf lupine has “pea-like” flowers. There are five petals, an upright petal known as the banner, two side petals called wings with the two remaining petals fused at the lower edge into a keel shape. The blue to lilac flowers have 5 sepals. The 10 stamens are hidden in the keel. Nine of the stamens are fused into a tube while 1 stamen is free. The superior ovary is inside the tube created by the fused stamens. There is a white or pale yellow spot on the banner. The back of the banner petal is hairy as is the upper edge of the keel.
Like all legumes (members of the Pea Family), silverleaf lupine fruits are pods covered with silky hairs that split along 2 seams to reveal several seeds.
Other folk names for L obtusilobus are satin lupine, Shasta lupine and bluntlobe lupine. A synonym for this species is Lupinus ornatus var obtusilobus.
The genus name, Lupinus, derives from the Latin word for wolf. There seems to be as many ideas about the derivation of this genus designation as there are Lupinus species. I mention several of these suggestions in previous posts on lupines. I found another explanation recently: lupines were thought to rob the soil of nutrients in the same manner that a wolf would rob a farmer’s chickens. Not true! Since lupines are legumes they have nitrogen fixing bacteria on their roots and actually enrich the soil. Obtusilobus, the species, means blunted.
These silverleaf lupines were growing in August along the Summit Lake Trail in Lassen Volcanic National Park (California).