Lupinus sparsiflorus is one of the most common lupines in the Mojave and Sonoran deserts. The palmate leaves have a light covering of relatively long hairs, most noticeably along the margins and on the undersurface, while the stems and seed pods are generally more hairy; the hairs here both lie flat against the surface and spread outwards. Leaflets are quite narrow, approximately linear in shape.

Flowers are about half an inch long, colored a bluish shade of purple, crossed by slightly darker veins. The upper banner petal has a yellow patch at the center, with a white margin, and an irregular pattern of red dots. These lighter colors fade as the flower matures, becoming bluish, while the other petals become darker. The short flower stalks and the two-lobed calyx are also hairy, while the keel petal has a few hairs along its lower edge. The two calyx lobes are about equal in height, and the upper is deeply divided into two lobes. Flowers are borne on the upper 8 inches of the stems, and they have a regular spiral arrangement. The bright green fruits point upwards, have a sparse covering of long hairs, and are slightly constricted between the seeds.