Rhamnus purshiana (Cascara Buckthorn, Cascara, Bearberry, and in the Chinook Jargon, Chittam or Chitticum; syn. Frangula purshiana, Rhamnus purshianus) is a species of buckthorn native to western North America from southern British Columbia south to central California, and inland to western Montana. It is the largest species of buckthorn, occasionally growing up to 15 m tall, though more commonly a large shrub or small tree 5â€“10 m tall, with a trunk 20â€“50 cm in diameter. The bark is brownish to silver-grey with light splotching. The leaves are deciduous, alternate, clustered near the ends of twigs; they are oval, 5â€“15 cm long and 2â€“5 cm broad with a 0.6â€“2 cm petiole, dark shiny green on top, fuzzy and paler green below. The flowers are tiny, 4â€“5 mm diameter, with five greenish yellow petals; the flowering season is brief, disappearing by early summer. The fruit is a berry 6â€“10 mm diameter, bright red at first, quickly maturing deep purple or black, and containing three seeds. It grows in moist, acidic soils in the shady side of clearings or in the marginal forest understory, near the edges of mixed deciduous-coniferous forests. It typically grows as a second-generation tree after alders have colonized a barren plot of land.