Lupinus hirsutissimus is a species in the Fabaceae (Legume) family known by the common name stinging lupine. It is native to the coastal mountains of Baja California and California as far north as the San Francisco Bay Area, where it grows on dry mountain slopes, including areas that have recently burned. It is an erect annual herb growing 20 centimeters to one meter tall; it may exceed one meter in habitat recovering from wildfire. The stem and herbage are coated in long, stiff hairs that sting skin when touched. Each palmate leaf is made up of 5 to 8 leaflets up to 5 centimeters long and 1 or 2 wide. The flower cluster bears several flowers generally not arranged in whorls. Each flower is between 1 and 2 centimeters long and purple to dark pink in color with a yellowish to pinkish spot on its banner. The fruit is a hairy legume pod up to 4 centimeters long.