California Croton (Croton californicus)

The Endangered Species Act (ESA), which was signed by President Nixon in 1973, was a much more robust piece of legislation than any of its authors had either imagined or intended. Despite all the controversy it has generated over the years, repeated attempts to rewrite or amend it into oblivion, and incessant legal challenges, the ESA has endured as one of the most significant pieces of environmental legislation in history. To industry and many landowners, the ESA denies citizens just use of their lands. To many environmentalists, it doesn’t go far enough, permitting continued degradation of habitats essential for the continued survival of listed species.

The ESA emphasizes the protection and recovery of only listed species or those proposed for listing. It therefore ignores endangered or rare habitat types and populations at the limits of the range of otherwise common or widespread species. (September 2000, – The Meanings of Rarity – for definitions of rarity.) From an evolutionary perspective, such outliers are probably highly significant, representing remnant taxa that have persisted in the face of changing environmental conditions. Such populations may therefore possess greater genetic variability (heterogeneity) than the taxon as a whole. Consider, for example, the giant redwood (Sequoiadendron giganteum), which doesn’t even appear on the California Department of Fish and Game’sList of Special Plants. This significant “remnant” from another geologic time is not afforded protected status under the ESA.

California’sdiverse flora is so varied due to the expansion and contraction of alternate “waves” of the three main geofloras over the past 65 million years. Our flora, therefore, consists of elements from the more temperate north (Arcto-Tertiary), the xeric (dry) Great Basin (Madro-Tertiary), and the tropical south (Neotropical-Tertiary). Species from one geoflora that are left behind, so to speak, as the wave recedes, are relicts or remnants of a once more widespread flora. Such local anomalies have long been the source of fascination and interest among scientists and amateurs because they represent a glimpse into the past or simply because they appear out of place. While such species don’t meet the criteria for listing under federal or state law and are afforded no legal protection, they most certainly represent unique and potentially significant biological and genetic resources. But, unless they are identified as sensitive resources under local General Plans, impacts to such relictual populations are completely unregulated.

In the next few issues of this newsletter, I will focus on some of these local rarities. The San Francisco Peninsula is home to many. In coming weeks I will prepare a summary of the non-listed taxa still found in San Francisco County which are at the limits of their range. Here is the first installment.

California croton (Croton californicus) is a member of the Euphorbiaceae, the spurge family, which includes over 7,500 species in 300 genera worldwide. The family is mostly tropical, occurring in North and South America, Africa, Eurasia, and Australia. Commercially important members of the family include potted plants (poinsettia-Euphorbia pulcherrima, and numerous cactus-like succulents), castor oil (castor bean-Ricinus communis), tung oil (Aleurites spp.), rubber (Hevea brasiliensis), soap substitutes (Sapium spp.), purgatives (Jatropha curcas), and the infamous Mexican jumping bean (a seed of Sebastiania pringlei containing the larva of a moth that wiggles when warmed). Members of the family are famous for their white latex with caustic properties. (My dad once got sap of a euphorb in his eyes while taking cuttings, and he wound up in the hospital.)

The genus Croton is well developed, with about 300 species in Brazil alone and a worldwide distribution of nearly 1,000 species. The genus derives its name from the Greek word kroton, meaning “tick,” which its seeds resemble.

California boasts only two native species (compared to six in Arizona). Croton californicus inhabits sandy soils, dunes, and washes below 900 meters. It is widespread and common along the south coast and southern deserts of California, extending into Arizona and Baja California, where it is called vara blanca and el barbasco. California croton is found in coastal sage scrub, chaparral, desert scrub, and coastal strand habitats. It reaches its northernmost limits on the dunes of San Francisco and Antioch, where it is infrequently encountered. The species is recorded in the floras of Arizona, and the counties of San Diego, Santa Barbara, San Luis Obispo, Kern, Monterey, Santa Cruz, San Francisco, and Contra Costa. I have seen it in Riverside, San Bernardino, Imperial, and Ventura counties. In San Francisco, California croton was recorded historically from Lobos Creek, above Baker’sBeach, Lone Mountain, Pine Lake, Lake Merced, and the Bayview Hills. It can still be found at the Presidio dunes and on San Bruno Mountain. San Francisco is the type locality for the species, where it was collected and named Hendecandra procumbens by Eschscholtz in the early 1800s.

California croton is a mostly prostrate perennial herb. Its stems are multi-branched and covered with grayish-whitehairs. Gray-green leaves are one to two inches long, less than an inch wide, and oblong to elliptic in shape. When crushed, the leaves have a strong but pleasant aroma. The male and female flowers are inconspicuous, borne on separate plants in terminal racemes, and appearing June through November in our region, earlier in the southern parts of the state.

California croton is one of those ghost-like sand dwelling plants. Its grayish color and low, multi-branched form make it quite inconspicuous. From appearance, it might remind you of dove weed (Eremocarpus setigerus, a spurge), beach saltbush (Atriplex leucophylla), beach-bur (Ambrosia chamissonis), or even coastal sagewort (Artemisia pycnocephala). Crushed leaves of California croton were used by native Americans to stupefy fish and were applied as a hot poultice to treat rheumatic pain. A salve made by mixing the crushed or powdered dry leaves with tallow was also used as a pain reliever.

In the Bay Area, California croton is a relict of a habitat type that is itself a relict. The coastal dunes of the northern San Francisco Peninsula are unique. And the presence of California croton is further proof.