Fiesta Flower (Pholistoma auritum var. auritum)

Continuing our exploration of local rarities, there is one species that was, until recently, thought to have completely vanished from San Francisco County. Fiesta flower, so named because garlands of its leaves and blue-lavender blossoms were donned by young girls during Mexican celebrations, once occurred on Bayview Hill and in southeastern San Francisco. In their 1958 book A Flora of San Frandsco California, Howell, Raven, and Rubtzoff mention collections of fiesta flower made in 1892, but don’t indicate whether or not it was still present at time of publication. But in 1996, fairly extensive stands of fiesta flower were located on Yerba Buena Island, representing the last populations in the county.

Fiesta flower is a member of the waterleaf family (Hydrophyllaceae), which consists of some 20 genera and around 300 species. The family is especially well represented in the western United States, although members are also found in South America, central and southern Africa, Southeast Asia, and far eastern Russia. Other genera in the waterleaf family include Phacelia, Eucrypta, Emmenanthe (whispering bells), Nama (purple mat), Nemophila (baby blue eyes), and Eriodictyon (yerba santa).

Originally assigned to the genus Nemophila in 1833 by the English botanist John Lindley, fiesta flower was subsequently changed to Pholistoma auritum (Nils Lilja 1839), Ellisia aurita (Jepson 1943), then back to Pholistoma. California supports three native Pholistoma species.

Fiesta flower is an inhabitant of shaded slopes and deep canyons. It is found on coastal bluffs, talus slopes, woodlands, and streambanks. Along the coast, fiesta flower reaches its northernmost limit in Mendocino County, where it is known from a single collection on serpentine north of Willits. It is also rare in Sonoma County, where it is recorded from shaded slopes near Bouverie and the Trinity-Cavedale area. In Marin County, fiesta flower occurs only on Angel Island. South of San Francisco, fiesta flower is uncommon on shaded slopes of San Bruno Mountain near Brisbane, in the Santa Cruz Mountains, along Pescadero Creek and Stevens Creek, and near Saratoga. Further south, it occurs in Monterey, San Luis Obispo, Santa Barbara, and San Diego counties. Inland, fiesta flower is known from Lake and Tehama counties to Calaveras County in the central Sierra Nevada foothills and Kern County in the Tehachapi Mountains. In the East Bay, it grows on the Mount Hamilton Range, the East Bay Hills, and Mount Diablo. A different variety (var. arizonicum) occurs in the Sonoran desert scrub of Arizona and California.

Fiesta flower is a fleshy, prostrate annual with many brittle, coarse, loosely branched, angled stems, which have bristles or hooked prickles. Leaves are oblong in outline, two to six inches long, and have seven to thirteen lobes. Petioles are widely winged and clasp the stems. Flowers, which are about an inch in diameter and blue to purple with darker marks in the corolla throat, appear in March, solitary or in cymes.

The last remaining populations in San Francisco are on the western slopes of Yerba Buena Island, growing beneath coast live oak trees (Quercus agrifolia) and subject to cools winds and fog drip. Other plants associated with these stands include stinging phacelia (Phacelia maivifolia), oso berry (Qemleria cerasiformis), bee plant (Scrophularia californica), poison oak (Toxicodendron diversilobum), elderberry (Sambucus mexicana), and Pacific pea (Lathyrus vestitus var. vestitus).

I find it intriguing that the last known populations of fiesta flower in San Francisco and Marin counties occur on islands. The stands of fiesta flower on Yerba Buena Island are remnants of what is presumably a more widespread population on the northern San Francisco Peninsula. They have persisted despite the planting and colonization of invasive non-native species such as eucalyptus and French broom, road building, and development. Both the Yerba Buena Island and Angel Island populations represent important sources of seed for reintroduction into the appropriate mainland settings. For this reason alone, we are encouraging city administrators to incorporate this locally-unique biological resource into their long-term reuse plans for Yerba Buena Island.