Diablo sunflower (Helianthela castanea)

Taxonomically speaking, few families are capable of causing attacks of sweating, heart palpitations and nervous laughter as the sunflower family (Asteraceae). Grasses aside, the composites, with their complex inflorescences characterized by ray and disk florets, pappus, chaff and phyllaries, frequently cause one to abandon all hopes of reaching a successful conclusion when working through the key. We usually resort to asking someone who already knows the answer and accept it at that. The sheer number of taxa adds to the sense that a positive identification is nothing short of a miracle. After all, Asteraceae is the largest family of dicots, consisting of some 1,300 genera and 21,000 species worldwide. It is also the largest plant family in California. The Jepson Manual lists 710 native species and 155 naturalized species in 205 genera. Those of you who know their way around Munz’s A California Flora are aware of the fact that the sunflower family is divided into 12 tribes, a taxonomic division ignored in The Jepson Manual to avoid confusing the uninitiated (i.e., most of us).

But the family offers great rewards, providing us with a diversity of forms and colors unrivaled among vascular plants. Representatives range from the most diminutive of annuals to robust, long-lived shrubs and even a few tropical members that approach tree status. The family also includes some of our most notorious weeds, yellow star thistle and German ivy to name just two. And some or California’s rarest plants belong to the sunflower family. Of the 1,742 taxa listed in the CNPS’ Inventory of Rare and Endangered Vascular Plants of California, 222 (12.7%) belong to the Asteraceae.

Included in this list is Diablo helianthella (Helianthella castanea). This stout perennial produces abundant basal and cauline leaves arising from a woody caudex. It produces large, solitary heads 1-2 in. across and comprised of 13-21 bright yellow ray flowers up to 1 in. long. Flowers develop their full glory from April through June. It forms ground-hugging clumps up to a meter across. At first glance, one might confuse this species with one of the mule ears (Wyethia sp.), a closely related member of the Heliantheae tribe. Other members of the tribe include the true sunflower (Helianthus), balsam root (Balsamorhiza), encelia, and viguiera, found in the southern part of the state. Truth is, Diablo helianthella is distinguished from mule ears chiefly by having sterile ray flowers, not a characteristic that is readily recognizable to the casual observer.

Diablo helianthella most typically occurs in the ecotone between chaparral and grassland or woodland habitats. Its distribution is restricted to Alameda, Contra Costa and San Mateo counties. It is presumed extirpated from San Francisco and Marin counties.

The flora of San Francisco lists Diablo helianthella as having been recorded from the Bayview Hills in the late 1890s. It can still be found inhabiting grassy slopes on San Bruno Mountain above Harold Road in Brisbane. In the East Bay, it is relatively widespread occurring throughout the Diablo Range, and stretching from the East Bay Hills to south of Niles Canyon. Diane Lake’s excellent compilation of unusual and significant plants of Alameda and Contra Costa counties lists the species as occurring at 28 general locations.

Although not exceedingly rare, Diablo helianthella is considered by the U.S. Fish and Wildlife Service as a Species of Special Concern. It is on the CNPS’ List 1B: 3-2-3, indicating that it is rare, threatened or endangered in California, of restricted distribution, endangered in a portion of its range and that it is endemic to California. The species has no formal state status, although impacts to it should be addressed during the environmental review process, pursuant to the California Environmental Quality Act.

This spring, when you are out enjoying the floristic bounty that is ours, keep your eyes open for this beauty. It’s worth hiking that extra mile to add it to your life list.