Yellow Mariposa Lily (Calochortus luteus)

Based entirely on aesthetics, perhaps no other group of California’s native wildflowers incites more awe than the lilies. Maybe due to the fact that so many beautiful lily hybrids are available as cut flowers and garden bulbs, or because they are so infrequently encountered in the wild, it is always a special treat to come across lilies in the field. Looking over the gorgeous illustrations by Catherine Watters in Peggy Fiedler’s book Rare Lilies of California will quickly give you an idea of what I mean.

The Liliaceae (in the class Liliopsida or Monocotyledones, the monocots) is a large and tremendously diverse family, including some 3,500 species in 250 genera worldwide. Although widespread (occurring in temperate and tropical latitudes of the Americas, Africa, Europe, Asia, and Australia), many genera are highly restricted in their distribution. While most members of the Liliaceae are herbaceous-with swollen storage organs such as bulbs, corms, and rhizomes-the family also includes evergreen succulents and woody climbers. Over the years, taxonomists have assigned members of the Liliaceae into such separate families as the Agavaceae, Amaryllidaceae, Calochortaceae, Smilacaceae, and Trilliaceae. According to the Jepson Online Interchange, these families are not currently recognized and, for the time being, the Liliaceae remains intact.

California supports some 323 native lilies belonging to 34 genera. These include such familiar genera as Agave, Allium, Brodiaea, Calochortus, Chlorogalum, Dichelostemma, Erythronium, Fritillaria, Lilium, Trillium, Triteleia, Yucca, and Zigadenus. A few of the many familiar non-native members of the lily family include Agapanthus, Aloe, Asparagus, Asphodelus (asphodel), Cordyline (lily tree), Ipheion (spring star flower), Muscari (grape hyacinth), Narcissus (daffodil), Nothoscordum (false garlic), and Tulipa (tulip).
In California, the lilies contribute a disproportionate number of rare species. Of the 2,101 taxa on the California Native Plant Society’s on-line Inventory of Rare and Endangered Plants, 115 (5.5%) belong to the Liliaceae. Eighty-four (73%) of these belong to just five genera: Calochortus (26 taxa), Allium (20 taxa), Fritillaria (15 taxa), Lilium (12 taxa), and Erythronium (11 taxa).

The genus Calochortus includes the mariposa lilies, globe lilies, fairy lanterns, star-tulips, and pussy ears. There are 58 described native taxa of Calochortus in California, out of a total of 70 taxa listed in the Flora of North America. Noted for their exceptionally beautiful flowers, these lilies are perennial, bulb-forming herbs, found in western North America and Central America. Many members of the genus possess highly varied nectaries (glands) on the petals. The generic name is derived from the Greek kalos (beautiful) and chortus (grass). Nearly 50 percent of the described taxa of Calochortus are considered rare, with one listed as threatened under the federal Endangered Species Act, two listed as rare under the State Endangered Species Act, one presumed extinct, 17 on CNPS List 1B (rare, threatened, or endangered), one on CNPS List 3 (more information needed), and four on CNPS List 4 (limited distribution).

Yellow mariposa lily is a widespread species with deep yellow, tulip-shaped flowers at the tips of stems up to 18 inches tall. The flowers, which may appear from April through June (late-May in San Francisco), often have a hairy, reddish-brown blotch near the center of the petals. It can be found on heavy soils in grasslands, woodlands, and mixed evergreen forests below 2,300 feet in elevation. It is distributed in coastal California from Santa Barbara to Humboldt counties, and inland from Tulare to Tehama counties. It has also been recorded east of the Sierra Nevada in Inyo County.

Calochortus luteus is the only member of the genus recorded from San Francisco County. In A Flora of San Francisco, California (1958), Howell, Raven, and Rubtzoff cited recorded locations from the Potrero Hills and Hunters Point. Chapter board member Margo Bors discovered and has been monitoring the last remaining populations of yellow mariposa lily left in our chapter area. One population of about 60 plants is located on serpentine in Starr King Open Space, a three-and-a-half-acre grassland community park on Potrero Hill, west and south of Starr King School. The Hunters Point population, consisting of as many as 1,000 plants, is located on a fenced serpentine hillside owned by PG&E, across Evans Avenue/Hunters Point Boulevard from the PG&E power plant and India Basin Shoreline Park. Yellow mariposa lily has not been recorded from San Bruno Mountain, but it is fairly common elsewhere on the San Francisco Peninsula, in Marin County, and in the East Bay.

Calochortus luteus is not listed under the state or federal Endangered Species acts, nor is it listed as rare by CNPS. However, due to its restricted occurrence, it is regarded as a species of local significance by the CNPS Yerba Buena Chapter.

As I write this in mid-April, it’s still raining and cold. I just returned from the eastern Mojave, where I had to flee a blizzard among the chollas and Joshua trees. Perhaps by the time you read this in June, there will still be time to see this lovely spring blossom on our grassy hillsides.