San Diego Thornmint

Acanthomintha ilicifolia is a petite annual herb growing up to about 15 centimeters (6 in) in maximum height. It has rounded to oval serrated leaves up to 1.5 cm (5⁄8 in) long. The inflorescence is a cluster of flowers with oval-shaped bracts nearly a centimeter long which are edged with long spines. Each flower is about a centimeter wide and white, often tinted purple to pink, with a hooded upper lip and a slightly longer lower lip. The flowers of the San Diego thornmint distinguish it from the other members of its genus by the hairless anthers and style. It germinates in late winter, flowers in April–May, and sets its seeds in June–July. Each flower can produce a maximum of 4 seeds, with each plant producing between 70 and 200 seeds. The species has been shown to have a seed bank. Seed age is associated with germination, with higher rates of germination recorded among older seeds.

This species is generally limited to San Diego County, California, and select areas of Baja California, Mexico. The distribution is higher in the United States, with over 80 historical occurrences listed in 2009 versus 13 occurrences in Mexico. It is found in chaparral, coastal sage scrub, and grassland habitats. It grows in gabbro and calcareous clay soils, usually on gentle slopes between 15 and 20 degrees.

While relatively little is known about the pollination of the species, it is believed to be pollinated by bees and checkered beetles. Two other members of the Acanthomintha genus, the San Mateo thornmint (Acanthomintha duttonii) and heartleaf thornmint (A. obovata ssp. cordata), are known to self-pollinate, and there is evidence of this for the San Diego thornmint as well.