Acanthomintha obovata ssp. duttonii (Flowering Plants)

Species Description

The San Mateo Thornmint is an aromatic annual herb in the mint (Larniaceae) family. It is a small annual species, usually less than 20 cm tall. It blooms from April through June. The species only grows on moist seeps in serpentine grasslands in San Mateo County. The flowers are white and tinged with lavender and grow in tight clusters surrounded by a nearly round, small, leaf-like or scale-like structures (bracts) with prominent spines. No other species with a similar appearance grows within the range of San Mateo Thornmint.

The species was protected as endangered under the federal Endangered Species Act in 1994. The San Mateo Thornmint is “endemic” to San Mateo County, which means it cannot be found naturally anywhere else in the world. It also means that the species has a limited geographic range. Thus the loss of even a few populations of this species could spell trouble for its continued existence.

Unfortunately, that is precisely what happened. At least five historical occurrences of the species have already been destroyed by development or habitat loss. Only one natural population exists today, and this population is within the legislative boundary of the GGNP.

This single remaining population has been in serious decline over the last few years. An estimated 53,000 individuals in 1994 had dropped to only 500 in 2007. The managers of the area where this population is found have been unable to arrest or adequately explain why this decline has occurred. The population is now so imperiled that the managers believe that even a low number of additional visitors could damage the plant by compacting soil or introducing weed seeds.

Because the site is off-trail in a remote area, sightings of San Mateo thornmint will not be counted in the Big Year contest as viewing this species would violate the Endangered Species Big Year Ethical Principles. The only way to check this species off your Big Year list is to attend special Big Year-sanctioned trips to see individual plants from nurseries within the GGNP.

Conservation Action Item

Restore Thornmint habitat:
Volunteer at Edgewood County Park

The San Mateo Thronmint is threatened by urbanization, alteration of drainage patterns, and presently by non-native plant invasion. Italian ryegrass, Lolium multiflorum, has been particularly problematic at the San Mateo Thornmint’s last remaining site. You can help the San Mateo Thornmint recover by volunteering at Edgewood County Park.

Big Year Competitors have reported 0 sightings and taken 3 actions to help this species recover so far this year.

Trips

• None scheduled