(Banner photo by Franco Folini)
Western Leatherwood (Dirca occidentalis) is a species of shrub in the family Thymelaeaceae which can reach a height of over three meters. Being deciduous, its bright green, ovate-shaped leaves senesce and drop in the winter. The small yellow flowers of this plant develop into yellow-green berries.
This plant is not only endemic to California, but to the Bay area specifically. It occurs most prevalently in Marin, San Mateo, Santa Clara, and Alameda counties.
The western leatherwood can be found in a variety of habitats. These include riparian zones, woodlands, evergreen and deciduous forests, chaparral, and scrubland. It typically inhabits an elevational range between 50 and 450 meters.
The western leatherwood usually blooms from January to March. The flowers of this species are often visited by Anna’s Hummingbirds (Calypte anna). They are also frequented by the introduced European honey bee (Apis mellifera). The plant’s very low dispersal rate may suggest that its natural disperser may be extinct or extirpated from the region. Due to its highly pliable branches, Dirca has historically been used by Native Americans for basket making.
Like many species, D. occidentalis is imperiled by habitat destruction. This threat poses a greater risk to Dirca than to other plants due to its extremely restricted range. Western leatherwood also features very low rates of growth, dispersal, and germination which limits how quickly populations can recover from losses. This species is considered to be a relic from a time where cooler, wetter conditions were more extensive in this part of California.
Western Leatherwood at Stanford
Small populations of Dirca exist in the northern portions of Stanford’s lands. They inhabit shaded woodlands which are protected from development. However, the population-limiting features of this species still make its long-term existence at Stanford unsure in the face of climate change and fire risk.