Acanthomintha duttonii is a species of annual plant endemic to San Mateo County, California in the family Lamiaceae.

It is commonly called San Mateo thornmint[1][2][3] and is found growing on serpentine soils near the Crystal Springs Reservoir in a six-mile (10 km) long strip on the east side of Montara Mountain at elevations of approximately 150 to 300 meters.

The species is named in honor of Harry Arnold Dutton, who in 1949 located a patch of another rare plant Cupressus abramsiana on nearby Butano Ridge.

The range of this species is sharply limited within a portion of central San Mateo County on the eastern lower slopes of the Santa Cruz Mountains.

[7] The single remaining large population, in Edgewood County Park, is a relict of a more extensive colony damaged by off-road motor-vehicle use.

Other native species that grow in the same area include Nassella pulchra, Delphinium hesperium, and Hemizonia congesta var.

San Mateo thornmint populations occupy slopes or flatland with deep, heavy clay soil inclusions.

Several factors contribute to serpentine soils being inhospitable to plant growth including a low calcium-magnesium ratio, lack of essential nutrients namely nitrogen, potassium, and phosphorus, and high concentrations of heavy metals.

Significant threats to A. duttonii identified in 1989 to 1998 were continuing urbanization of the San Francisco Peninsula,[9] an inherently fragmented population and off-road vehicle use.