[floranorthamerica.org] Channel Islands Endemic, Variations, Recovery from Overgrazing: Castilleja hololeuca is endemic to the four major islands of the northern Channel Islands. It is similar to C. lanata, a mostly Mexican species that reaches Arizona, New Mexico, and southwest Texas. However, C. hololeuca appears to be more closely related to C. foliolosa, a species of the California mainland. These three species, and C. galehintoniae G. L. Nesom of Nuevo León, all share a distinctive, thick indument of pale, matted, and often branched hairs on the stems and leaves. Large individuals of C. hololeuca form thick, woody trunks. On Anacapa Island, closest to the mainland, red-flowered forms of C. hololeuca predominate. On Santa Cruz Island, to the west, both red- and yellow-bracted forms are fairly common, usually in separate populations. Further offshore, on San Miguel and Santa Rosa islands, most plants are yellow to, occasionally, peach in coloration. Reports of this species from Santa Barbara and Santa Catalina Islands are referable to other species, mostly C. foliolosa. Populations of C. hololeuca historically declined from grazing by introduced game and livestock species. The plants are recovering well, following removal of the grazing animals, and are now common in many areas, especially on San Miguel Island. (link added by Mary Ann Machi)