Calochortus dunnii
Dunn's Mariposa Lily

The lily genus Calochortus contains some of California's rarest plants. Calochortus dunnii is one of these, state-listed as Rare. It is restricted to gabbro and metavolcanic soils of the Peninsular Ranges of San Diego County and northern Baja California. Unusual soil types like gabbro often support species of plants--called edaphic endemics--which grow only on that type of soil, or on a few similar types of soil. Experienced botanists often use soil maps to seek out likely places to find these often rare endemics.

Gabbro is a dark-colored plutonic rock which degrades into a reddish-brown, iron- and magnesium-rich, clay soil. Because the gabbro rocks break down readily, these areas are usually strewn with loose rubble, rather than having the large granitic boulders that characterize most of the mountain range.

These photos were taken on the west slope of Cuyamaca Mountain, where this lily grew along with two other gabbro endemics, Pickeringia montana and Salvia sonomensis. Other known sites for C. dunnii are elsewhere in the Cuyamaca and Laguna Mountains, as well as Guatay Mountain, San Miguel Mountain, and Otay Mountain.

Calochortus dunnii has a few basal leaves, which wither early, and a slender, branched flower stalk reaching to over half a meter in height. The flowers are erect and bell-shaped with broad white petals, sometimes flushed with pink. Each of the petals has a reddish-brown blotch above the round nectar gland, and is yellow-hairy near the nectary. Seed capsules are held vertically.

For more information, see:
Beauchamp, R. Mitchel. A flora of San Diego County, California. Page 28.
Oberbauer, Thomas. Soils and plants of limited distribution in the Peninsular Ranges. Fremontia 21:3-7, October 1993.
Schoenherr, Alan. The Natural History of California. UC Press. Pages 49, 100, 278-80, 320.