''Calochortus tiburonensis'', the Tiburon Mariposa lily, is a rare member of the genus ''

Calochortus ''Calochortus'' is a genus of flowering plants in the lily family. The group includes herbaceous, perennial and bulbous species, all native to North America (primarily the Western United States). The genus ''Calochortus'' includes mariposas ( ...

'' in the family

Liliaceae The lily family, Liliaceae, consists of about 15 genera and 610 species of flowering plants within the order Liliales. They are monocotyledonous, perennial, herbaceous, often bulbous geophytes. Plants in this family have evolved with a fai ...

. It is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

Marin County, California Marin County ( ) is a County (United States), county located in the northwestern part of the San Francisco Bay Area of the U.S. state of California. As of the 2020 United States census, 2020 census, the population was 262,231. Its county seat a ...

, where it is known only from one population on Ring Mountain east of

Mill Valley Mill Valley is a city in Marin County, California, United States, located about north of San Francisco via the Golden Gate Bridge and from Napa Valley. The population was 14,231 at the 2020 United States census, 2020 census. Mill Valley is lo ...

. There it occurs on a single serpentine outcrop in grasslands from in elevation.

Description

''Calochortus tiburonensis'' is a

perennial In horticulture, the term perennial ('' per-'' + '' -ennial'', "through the year") is used to differentiate a plant from shorter-lived annuals and biennials. It has thus been defined as a plant that lives more than 2 years. The term is also ...

growing from a

bulb In botany, a bulb is a short underground stem with fleshy leaves or leaf basesBell, A.D. 1997. ''Plant form: an illustrated guide to flowering plant morphology''. Oxford University Press, Oxford, U.K. that function as food storage organs duri ...

to 10–60 cm in height with a single leaf. It produces anywhere from 2 to 7 erect flowers annually on a branching stem. The ciliate, light yellow-green

petal Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...

s are streaked with purplish-brown. When mature, ovaries form a capsule full of small, dark brown seeds.Flora of North America, ''Calochortus tiburonensis''
/ref>

Conservation

The plant was federally listed as a threatened species in 1995.USFWS
Determination of endangered status for ten plants and threatened status for two plants from serpentine habitats in the San Francisco Bay region of California.
''Federal Register'' February 3, 1995. It is considered threatened due to loss of surrounding habitat to recreational activities, to competition from invasive plant species, to its proximity to a dense population center, and to its confinement to a single population of plants. The population grows on land owned by the Marin County Open Space District,C. Michael Hogan. 2008
''Ring Mountain'', The Megalithic Portal.
ed. Andy Burnham an area previously owned and preserved by

The Nature Conservancy The Nature Conservancy (TNC) is a global environmental organization headquartered in Arlington, Virginia, United States. it works via affiliates or branches in 79 countries and territories, as well as across every state in the US. Founded in ...

. It was first brought to the attention of science in 1971, and was described to science in 1973.Hill, A. J. (1973). A distinctive new ''Calochortus'' (Liliaceae) from Marin County, California. ''Madroño'' 22:100-104. It is protected along with a number of other rare

serpentine soil Serpentine soil is an uncommon soil type produced by weathered ultramafic rock such as peridotite and its metamorphic derivatives such as serpentinite. More precisely, serpentine soil contains minerals of the serpentine subgroup, especially an ...

s endemic plants that grow on and around Ring Mountain. The plant has probably always been rare and limited to its current distribution on the Ring Mountain outcrop. A 1991 estimate placed the total population size at about 40,000 individuals.The Nature Conservancy
/ref> While the land is protected, the flora upon it are still vulnerable to events such as

wildfire A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a ...

s or

drought A drought is a period of drier-than-normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, ...

, and to damage from off-leash dogs, hikers,

cyclists Cycling, also known as bicycling or biking, is the activity of riding a bicycle or other types of pedal-driven human-powered vehicles such as balance bikes, unicycles, tricycles, and quadricycles. Cycling is practised around the world for pur ...

vandals The Vandals were a Germanic people who were first reported in the written records as inhabitants of what is now Poland, during the period of the Roman Empire. Much later, in the fifth century, a group of Vandals led by kings established Vand ...

, and wildflower collectors.

References

''Calochortus tiburonensis''
USDA, NRCS. 2006. The PLANTS Database, Version 3.5. Data compiled from various sources by Mark W. Skinner. National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

External links

''Calochortus tiburonensis'' — Calphotos Photo gallery, University of California @ Berkeley
{{Taxonbar, from=Q5023121 tiburonensis Endemic flora of California Endemic flora of the San Francisco Bay Area Natural history of the California chaparral and woodlands Natural history of Marin County, California Tiburon, California Plants described in 1973 Critically endangered flora of California