FWS Focus

Overview

Characteristics
Overview

San Mateo thornmint is a fragrant herb in the mint family with white or purplish flowers and very spiny bracts, which are the leafy structures just beneath the flowers. It is only found in San Mateo County, California, and at the time of listing, was only known from a single population at Edgewood County Park and Natural Reserve, in San Mateo. Thanks to a reseeding and management project, there are now six populations: five at Edgewood Park and one north of the park at Pulgas Ridge. Four of these populations are stable or increasing in number.

This species was listed as endangered on September 18, 1985.

The plant continues to be threatened by:

  • Competition with non-native grasses, particularly in the absence of active habitat management
  • Deleterious chance events that reduce or eliminate populations
  • Changes to hydrological flows
  • Infestation by parasitic dodder (Cuscuta spp.)

Scientific Name

Acanthomintha obovata ssp. duttonii
Common Name
San Mateo thornmint
FWS Category
Flowering Plants
Kingdom

Location in Taxonomic Tree

Identification Numbers

TSN:

Characteristics

Characteristic category

Life Cycle

Characteristics
Reproduction

San Mateo thornmint is an annual herb, living less than one year. Flowers appear from April through June or July, with those lower on the stem typically opening first. Opening three to five hours after sunrise, the flowers remain open for two to four days. San Mateo thornmint is pollinated by generalist pollinators, including native bees. The plants can also reproduce by pollinating themselves, in which case pollinators are not necessary. Each plant can produce a large number of seeds. Seeds are thought to require six months of dormancy after they fall and can survive at least 2.5 years in the soil.

Characteristic category

Similar Species

Characteristics
Similar Species
Characteristic category

Habitat

Characteristics
Habitat

San Mateo thornmint is only found in San Mateo County. It grows on serpentine clay soils that fill fissures between other types of rock and soil. These clays have a low calcium/magnesium ratio, as well as a high moisture content. General community associates include chaparral and valley foothill grassland plants.

Grassland

Land on which the natural dominant plant forms are grasses and forbs.

Characteristic category

Physical Characteristics

Characteristics
Size & Shape

San Mateo thornmint is a strongly scented annual herb of the mint family (Lamiaceae). The plant can grow up to 8 inches tall and is typically unbranched. It has a squarish stem and opposite leaves. The oblong leaves are small, between 0.3 to 0.5 inches, and may be toothed. The flowers are white or sometimes tinged with lavender and grow in tight clusters surrounded by very spiny bracts, which are small scale-like leaves that grow beneath the base of the flowers.

Geography

Characteristics
Range

At the time of listing, San Mateo thornmint was only known from a single population at Edgewood County Park and Natural Reserve in San Mateo. Thanks to a reseeding and management project, there are now six populations: five at Edgewood Park and one north of the park at Pulgas Ridge. Four of these populations are stable or increasing in number.

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