Acanthomintha ilicifolia

Acanthomintha ilicifolia San Diego thornmint
Conservation status
ESA )
Critically Imperiled  (NatureServe)[1]
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Lamiales
Family:	Lamiaceae
Genus:	Acanthomintha
Species:	A. ilicifolia
Binomial name
Acanthomintha ilicifolia A.Gray

Acanthomintha ilicifolia, known by the common name San Diego thornmint, is a rare species of flowering plant in the mint family. It is native to Baja California and San Diego County, California, where it is a resident of the chaparral and coastal sage scrub plant communities and vernal pools.^[2]

Acanthomintha ilicifolia has been

Acanthomintha ilicifolia is a petite annual herb growing up to about 15 centimeters (5.9 in.) in maximum height.[3] It has rounded to oval serrated leaves up to 1.5 (0.59 in.) centimeters 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.^[4]

Life History

The San Diego thornmint is an annual plant that germinates in late winter, flowers in April–May, and sets its seeds in June–July.^[5] Each flower can produce a maximum of 4 seeds, with each plant producing between 70–200 seeds.^[6] The species has been shown to have a seed bank.^[4] Seed age is associated with germination, with higher rates of germination recorded among older seeds.^[4]

Ecology

Pollinators

While relatively little is known about the pollination of the San Diego thornmint, 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.^[4][7]

Habitat

The San Diego thornmint is found in chaparral, coastal sage scrub, and grassland habitats. It grows in gabbro and calcareous clay soils, usually on gentle slopes between 15-20 degrees.^[3][5]

Range

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.^[2][5]

Conservation

Population Size

As of 1998, the population of the San Diego thornmint is estimated to be between 150,000 and 170,000. Most occurrences have between 100-10,000 plants, with the largest occurrence boasting 60,000 in 1993. When the species was listed under the ESA in 1998, there were an estimated 52 known occurrences of the plant in the United States and 9 in Mexico, and 32 known extant occurrences. At the time of the 2009 5-year review, estimates identified around 80 known occurrences with approximately 55 extant occurrences.^[2]

Past and Current Geographical Distribution

Seed dispersal for the San Diego thornmint is limited, so the range of the species has remained largely the same. Although more occurrences of the plant have been found since it was listed under the ESA, it is likely that they existed before.^[2]

Major Threats

Major threats toward the San Diego thornmint fall into five categories:^[2]

Factor 1: Destruction or modification of habitat

This is the most significant factor affecting the species. Older threats that have since lessened in significance include mining operations that alter soil state. Newer threats include destruction by fire and invasive species. Some of the most common invasive species in the habitat are

The San Diego thornmint was listed as endangered under the California Endangered Species Act in January 1982. It was federally listed as threatened under the ESA on October 13, 1998.[2]

5-Year Review

5-year reviews have been initiated in 2008, 2010, 2013, and 2021. Only one 5-year review has been published in 2009. The review compiled scientific data concerning the thornmint’s conservation status and recommended cooperation between state and landowners to continue effective conservation. The review also recommends a status change to level “8”, having moderate threats with a high likelihood of recovery. The overall degree of severity was reduced and may be the reason why further 5-year plans have not been published.^[2]

The 5-year review found that only 2 occurrences of the San Diego thornmint have gone extinct since its listing under the ESA in 1998. In addition, 39 of the estimated 55 extant occurrences are protected in conserved areas, compared to 7 at the time of listing. The review points to working with private landowners to conserve the remaining 16 occurrences as an important step in conservation of the species.^[2]

Recovery Plan

There is not currently a formal species status assessment or recovery plan for the San Diego thornmint. In 2008, the U.S. Fish and Wildlife Service designated 641 acres of both private and state/federal land in San Diego County as “Critical Habitat” for the San Diego thornmint.^[8]

Recent efforts to conserve the San Diego thornmint, such as the San Diego Thornmint Expansion Project,^[9] focus on reducing the impact of invasive species, habitat loss, and climate change. Studies on the pollination^[7] and gene flow^[6] of this species are also important for conservation and expansion of the plant into new areas.

References

External links

• Calflora Database: Acanthomintha ilicifolia (San Diego thorn mint)
• Jepson Manual eFlora treatment of Acanthomintha ilicifolia
• USDA Plants Profile for Acanthomintha ilicifolia (San Diego thorn mint)
• Sierra Club, San Diego Chapter: Profile of Acanthomintha ilicifolia (c.1994)
• "San Diego Thornmint". U.S. Fish and Wildlife Service.
• UC Photos gallery — Acanthomintha ilicifolia