The California buckthorn (Rhamnus californica, syn. Frangula californica (Eschsch.) A.Gray) is also called coffeeberry because its berries contain seeds which look like coffee beans. It is a fairly common plant native to California and southwestern Oregon
It is an evergreen shrub growing to 2-5 m tall, with dark red branches. The leaves are 2-8 cm long, dark, dull green, and curl under at the edges. The flowers are small and greenish-white with five petals; they are produced in clusters of 5-60 together. The fruit is a berry 10-15 mm diameter, which turns red, then purple and finally black over the summer
Coffeeberry plants grown in windy or exposed areas usually do not exceed a meter or two in height or width, but individuals growing in inland areas or sheltered canyons can spread to 8 m wide. The plant is found in shrubby coastal chaparral areas, foothill slopes, and oak woodlands in most regions in California west of the Sierra Nevada, and at altitudes of up to 2300 m.
There are two subspecies:
Rhamnus californica subsp. californica - widespread in western California. Fruit with two seeds; twigs red; leaves with conspicuous veins.
Rhamnus californica subsp. occidentalis - northern California and southwest Oregon, on serpentine soils. Fruit with three seeds; twigs brown; leaves with inconspicuous veins.