Lupinus diffusus (Oak Ridge lupine, spreading lupine, or sky-blue lupine) is a species of lupine native to the southeastern United States, from North Carolina south to Florida and west to Mississippi. It is restricted to very dry, sandy soils, often in open pine or oak woodlands.

It is a perennial herbaceous plant growing to 30–50 centimetres (12–20 in) tall. The leaves are palmately compound with 3-5 leaflets 6–12 centimetres (2.4–4.7 in) long and 3–5 centimetres (1.2–2.0 in) broad, gray-green to silvery green, covered with fine white hairs. The flowers are pale blue or violet, produced in a dense spike 15–30 centimetres (5.9–11.8 in) long.