Tiburon Mariposa Lily

(Calochortus tiburonensis)

Tiburon mariposa lily is a California threatened plant species, which means that killing or possessing plants from wild populations is prohibited by the California Endangered Species Act (CESA). This species is also listed as threatened under the federal Endangered Species Act. Tiburon mariposa lily is bulb-forming perennial herb in the lily family (Liliaceae). It grows to about 20 inches tall, is usually branched, and produces two to three flowers at the end of each branch. Flowers are light yellow-green with reddish to purplish-brown markings, and have long slender hairs on the upper surface and margins of the petals.

Tiburon mariposa lily is only known to occur at the Ring Mountain Preserve on the North end of the Tiburon peninsula, which is managed by Marin County Open Space. The population is distributed over three major colonies, with population sizes reported from hundreds of plants in 1986 to greater than 30,000 plants in 1995 according to the California Natural Diversity Database. Tiburon mariposa lily grows on serpentine and serpentine derived soils in open areas in a serpentine bunchgrass community. Associated species include serpentine reed grass (Calamagrostis ophitidis), Tiburon buckwheat (Eriogonum luteolum var. caninum), and purple needle grass (Stipa pulchra). It also grows in association with two other state and federally listed species, Tiburon paintbrush (Castilleja affinis ssp. neglecta) and Marin western flax (Hesperolinon congestum).

Tiburon mariposa lily is vulnerable to extinction from stochastic events such as fire, severe drought, pest or disease outbreak, or other natural or human-caused disasters due to its restricted range. It is also threatened by competition from non-native invasive plant species and trampling from recreational activities. The Ring Mountain Preserve has a management plan and monitoring program, and actions are taken annually to control non-native invasive plant species. Although the Ring Mountain Preserve population is secure, long-term funding for management and monitoring is not guaranteed.

Annual population monitoring and non-native invasive plant control efforts should continue at Ring Mountain Preserve to ensure the conservation of Tiburon mariposa lily. Informative signs should be placed at the preserve entrances that describe the effects of off-trail use on rare plants. In addition, efforts to place bulbs and seeds into long-term conservation storage should be explored to reduce the threat to the species from stochastic events.

CDFW may issue permits for Tiburon mariposa lily pursuant to CESA, and you can learn more about the California laws protecting Tiburon mariposa lily and other California native plants. Tiburon mariposa lily occurs in CDFW’s Bay Delta Region. More information is also available from the U.S. Fish and Wildlife Service Species Profile for Tiburon Mariposa Lily.

Updated 01/14/2014

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Calochortus tiburonensis, © Rick York and CNPS
Calochortus tiburonensis, © Rick York and CNPS
Calochortus tiburonensis CDFW illustration by Mary Ann Showers, click for full-sized image
Calochortus tiburonensis CDFW illustration by Mary Ann Showers, click for full-sized image