CPC Plant Profile: San Diego Thornmint
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Plant Profile

San Diego Thornmint (Acanthomintha ilicifolia)

Photo Credit: Kier Morse
Description
  • Global Rank: G1 - Critically Imperiled
  • Legal Status: Federally Threatened
  • Family: Lamiaceae
  • State: CA
  • Nature Serve ID: 151284
  • Date Inducted in National Collection: 02/09/1992

San Diego thornmint is an annual aromatic herb in the mint family (Lamiaceae). From April to June, it produces clusters of white, two-lipped, tubular flowers with pink markings on the lower lip. It has sharp spiny bracts (modified leaves) protecting the whirls of flowers, and can grow to 12 inches in height. Unfortunately, over ninety percent of the available habitat for this species has been lost to development over the past century and non-native invasive plants and climate change continue to threaten the species.

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    Updates
    Katie Heineman
    • 02/04/2021
    • Propagation Research

    San Diego thornmint (Acanthomintha ilicifolia) has been extirpated from a historical population at Ramona Grasslands since around 2010. To investigate if this species persists in the soil seed bank, Stacy Anderson and the San Diego Zoo Native Plant Seed Bank collected soil core samples from 15 locations surrounding a post marking the last observed "clump" of plants at that site. We took two depths of samples at each location: 0-3 cm and 0-9 cm. We found that we were unable to accurately take soil cores for successive depths due to the crumbly nature of the clay lens soil on which this species grows. We left the samples to vernalize for 3 months and then we recently potted the samples with vermiculite in 8 in pots to observe germination. 

    • 10/16/2020
    • Demographic Research

    San Diego thorn-mint (Acanthomintha ilicifolia) Mitigation Projects, San Diego, CA. Robert S. Taylor, Jr. collected baseline ecological and demographic data on this state endangered plant species as part of five year monitoring program. Monitored six natural populations and three artificially created populations. Analyzed density, vigor and reproductive parameters to assess population viability. Dr. Ellen Bauder seems to be the one person doing research on the species. She is at San Diego State University. (Bauder 1994)

    • 10/16/2020
    • Propagation Research

    In 2014, Stacy Anderson with SDZG led a common garden study comparing seeds, germination, growth habit, and reproduction of 6 different populations of thornmint from throughout the county.

    • 10/16/2020
    • Propagation Research

    In 2014, Stacy Anderson with SDZG led a common garden study comparing seeds, germination, growth habit, and reproduction of 6 different populations of thornmint from throughout the county.

    • 10/16/2020
    • Propagation Research

    Common garden studies at SDZG showed that the species is easily propagated and produces copious amounts of seed when grown in a controlled setting.

    • 10/16/2020
    • Genetic Research

    "This endemic is genetically complex, revealing significant differentiation of neutral and potentially adaptive genetic variation among populations, and possessing at least two cytotypes, sometimes even within the same population.

    • 10/16/2020
    • Seed Collection

    In 2017, SDZG made maternal line seed collections from 4 populations in San Diego County. 2 of these collections are going to be used as part of a seed bulking project. When grown in a controlled setting this species produces copious amounts of seed. Through this bulking project 10's of thousands of seeds will be available for augmentation of managed populations, and potentially for introduction into new or historic locations. Maternity will be tracked, and unless research directs us otherwise, the genetic diversity of different populations will be kept separate.

    • 10/16/2020
    • Seed Collection

    In 2018, SDZG made three new seed collections of Acanthomintha ilicifolia in San Diego County. 12,400 seeds were counted from 238 maternal lines in 9 sub-populations within the three locations. These will be added to the seed bulking project and kept for research and future species recovery projects.

    • 09/01/2020
    • Orthodox Seed Banking

    Based on an September 2020 extract of the California Plant Rescue Database, San Diego Zoo Global holds 15 accessions of Acanthomintha ilicifolia in orthodox seed collection. There are as many as 151907 seeds of this species in their collection - although some may have been used for curation testing or sent to back up.

    • 09/01/2020
    • Orthodox Seed Banking

    Based on an September 2020 extract of the California Plant Rescue Database, California Botanic Garden holds 17 accessions of Acanthomintha ilicifolia in orthodox seed collection. There are as many as 1734339 seeds of this species in their collection - although some may have been used for curation testing or sent to back up.

    • 08/05/2020
    • Seed Collection

    Based on an August 2020 extract of the California Plant Rescue Database, San Diego Zoo Global has collected 15 seed accessions of Acanthomintha ilicifolia from 10 plant occurrences listed in the California Natural Diversity Database. These collections together emcompass 1191 maternal plants

    Emily Burson
    • 01/24/2019

    "This endemic is genetically complex, revealing significant differentiation of neutral and potentially adaptive genetic variation among populations, and possessing at least two cytotypes, sometimes even within the same population. While additional study is required to resolve the extent of potential local adaptation in this species, conservation plans should limit the movement of germplasm among occurrences and monitor populations in order to limit potential long-term impacts to population viability. Given that these findings challenge the canonical model of genetic structure in rare plants (low genetic variation and limited genetic structure), we recommend guidelines to apply genetic information to conservation strategies".

    Emily Burson
    • 01/24/2019

    In 2018, SDZG made three new seed collections of Acanthomintha ilicifolia in San Diego County. 12,400 seeds were counted from 238 maternal lines in 9 sub-populations within the three locations. These will be added to the seed bulking project and kept for research and future species recovery projects.

    Joe Davitt
    • 10/18/2017

    In 2014, Stacy Anderson with SDZG led a common garden study comparing seeds, germination, growth habit, and reproduction of 6 different populations of thornmint from throughout the county.

    Joe Davitt
    • 08/16/2017

    As of 2017, invasive species and climate change pose the largest threat to this species. While development, grazing, and trampling were certainly causes of a massive decline in population and threats at time of listing, these threats have been minimized as the species is now protected by the San Diego Multiple Species Conservation Program (MSCP) and by the laws afforded to state and federally listed endangered species. Most populations are well documented, monitored, and recreational activities are managed where necessary. Invasive grasses and non-native forbs can completely cover clay lenses, leading to reduced light, water competition, and the development of thatch. This can also lead to increased fire-frequency. Rainfall and temperature affect germination and successful reproduction in A. ilicifolia and climate change threatens to alter these factors in the future. It is believed that the soil seed bank of this species is relatively small, and potentially short-lived. Prolonged drought (thought to be more common as a result of climate change) could lead to a drastic decline in numbers, resulting in inbreeding depression, genetic bottle-necks, and/or occurrence extirpations.

    Joe Davitt
    • 08/16/2017

    With many of the known occurrences on conserved land, research should focus on weed removal strategies, seed reintroduction strategies, seed viability studies, soil seed bank longevity studies, etc. Common garden studies at SDZG showed that the species is easily propagated and produces copious amounts of seed when grown in a controlled setting. Seed bulking from wild collected seed could allow for the augmentation of well managed populations. It is also possible to reintroduce seed into historic locations with extirpated populations. Weed removal will be key to the success of any reintroduction/augmentation plan. John Ekhoff with the California Department of Fish and Game has had great success in controlling weeds at the Hollenbeck Wildlife Area occurrence, and the population is doing very well (as of 2017).

    Joe Davitt
    • 08/16/2017

    Per USFWS 2009 report:
    39 of the 55 extant occurrenes of Acanthomintha ilicifolia are conserved. Eight of the conserved occurrences are on land owned and managed by the Cleveland National Forest. Eight are on land owned or partially owned by the State of California. Eight are on land owned or managed by local governments; two by the County, five by the City of San Diego, and one by the City of San Marcos. Eighteen conserved occurrences are on privately owned lands. Seven of these occurrences are on lands that receive minimal management because they are managed by home owners associations or they are on conserved lands where the conservation of A. ilicifolia is not the primary focus of the preserved land. The other eleven privately owned occurrences are managed by organizations focusing on the habitat and rare species conservation and who actively manage and monitor A. ilicifolia at these sites. Of these eleven occurrences, the Center for Natural Lands Management manages five occurrences; TNC manages two occurrences; The Back County Land Trust manages one occurrence; and the San Diego Habitat Conservancy manages two occurrences.

    Joe Davitt
    • 08/16/2017

    As of the 2009 USFWS report, 39 of the 55 extant populations were conserved.

    Joe Davitt
    • 08/16/2017

    As of the USFWS 5-year review in 2009, there were records for 80 historic occurrences with 55 known extant populations in San Diego County. 37 of the extant populations had recent survey data available while 13 had not been surveyed. At the time (2009) there were 13 historic occurrences in Baja Mexico, though no information on their status was available. At the time of listing (1998), an estimated 150,000-170,000 individuals were estimated. No estimate was given in 2009 but it was believed that there were likely a greater number of individuals, because more occurrences had been found. It is very difficult to estimate the number of living individuals of this species as the population numbers fluctuate greatly from year to year.

    Joe Davitt
    • 08/09/2017

    In 2017, SDZG made maternal line seed collections from 4 populations in San Diego County. 2 of these collections are going to be used as part of a seed bulking project. When grown in a controlled setting this species produces copious amounts of seed. Through this bulking project 10's of thousands of seeds will be available for augmentation of managed populations, and potentially for introduction into new or historic locations. Maternity will be tracked, and unless research directs us otherwise, the genetic diversity of different populations will be kept separate.

    Nature Serve Biotics
    • 05/02/2017

    Habitat loss and fragmentation are expected to continue with the development of southern California and northern Baja California. At least 40% of the historic known sites in the U.S. have been extirpated by residential and commercial development. Ongoing off-road vehicle use, trampling by cattle, erosion, and invasion by non-native plants are also threatening populations.

    Naomi Fraga
    • 01/01/2010

    Development (has destroyed 90% of suitable habitat for this species) Off-road vehicle use (including dirt bikes) Trampling by cattle and horses Invasion by exotic grasses and other non-native species (USFWS 1998)

    Naomi Fraga
    • 01/01/2010

    There are 150,000-170,000 individuals located in 32 populations, but only four of these are covered by the Multiple species Conservation Program (MSCP) in southern San Diego (USFWS 1998).

    Naomi Fraga
    • 01/01/2010

    San Diego thorn-mint (Acanthomintha ilicifolia) Mitigation Projects, San Diego, CA. Robert S. Taylor, Jr. collected baseline ecological and demographic data on this state endangered plant species as part of five year monitoring program. Monitored six natural populations and three artificially created populations. Analyzed density, vigor and reproductive parameters to assess population viability. Dr. Ellen Bauder seems to be the one person doing research on the species. She is at San Diego State University. (Bauder 1994)

    Naomi Fraga
    • 01/01/2010

    This species is covered in the San Diego Multiple Species Conservation Plan.

    Naomi Fraga
    • 01/01/2010

    This species needs new or restored suitable habitat to return to healthy numbers.

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    Photos
    Nomenclature
    Taxon Acanthomintha ilicifolia
    Authority (Gray) Gray
    Family Lamiaceae
    CPC Number 19
    ITIS 32426
    USDA ACIL
    Common Names San Diego Thornmint | San Diego Thorn-mint
    Associated Scientific Names Calamintha ilicifolia | Acanthomintha ilicifolia
    Distribution Acanthamintha ilicifolia is endemic to San Diego County and the tip of northwestern Baja California.
    State Rank
    State State Rank
    California S1
    Habitat

    Acanthomintha ilicifolia is restricted to gabbro and calcareous clay soils known as clay lenses. It occurs in openings in coastal sage scrub, chaparral, and native grasslands, but only where these lenses occur.

    Ecological Relationships

    Neighbors may include spring annuals, bulbous perennials, and neighboring common shrubs of scrub and chaparral habitats. Pollinator studies have shown the species to be pollinated by a wide range of insects including various bees, beetles, and butterflies. The species is restricted by soil type requirements, though soil microbe analysis have not been done.

    Pollinators
    Common Name Name in Text Association Type Source InteractionID
    Bees
    Sweat bees Agopostemon Confirmed Pollinator Link
    Chimney bees Ancyloscelis Confirmed Pollinator Link
    Honey bees Apis Confirmed Pollinator Link
    Bees Suspected Pollinator Floral Link
    Centris bees Ceratina Confirmed Pollinator Link
    Sweat bees Conanthalictus Confirmed Pollinator Link
    Chimney bees Diadasia Confirmed Pollinator Link
    Long-horned bees Exomalopsis Confirmed Pollinator Link
    Sweat bees Lasioglossum Confirmed Pollinator Link
    Butterflies & Moths
    Skippers Hesperiidae Floral Visitor Link
    Beetles
    Checkered beetles Checkered beetles Suspected Pollinator Floral Link
    Checkered beetles Cleridae Confirmed Pollinator Link
    Flower beetles Melyridae Floral Visitor Link
    Flies
    Bee flies Bombyliidae Floral Visitor Link
    Syrphid flies Syrphid flies Floral Visitor Link
    Other
    Thrips Thysanoptera Floral Visitor Link

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