Frangula purshiana aka Cascara Buckthorn

Frangula purshiana, or cascara, is a western North American tree. It belongs to the buckthorn family, Rhamnaceae. Its native range runs from western Canada to Durango, Mexico. Sources also call it Rhamnus purshiana, an older scientific name. It grows in rich bottomlands and along canyon sides. These sites often lie within conifer woods. It can form a tree or an upright, many-stemmed shrub.

One cultivation account gives a height of 33 feet [10 metres]. It gives a spread of about 20 feet [6 metres]. Larger trees can reach 50 feet [15 metres]. Shrub forms reach about 15 feet [4.5 metres]. Thin, gray-brown bark often bears pale patches of lichen. The yellow inner bark tastes bitter. Young twigs have soft hairs and a reddish-brown tint. The exposed buds lack scales and bear rusty hairs.

The leaves grow alternately along the stems and have simple blades. Their shape ranges from oval to oblong, with clear side veins. Dark green upper surfaces contrast with paler undersides. Leaf edges may be smooth, wavy, or finely toothed. Oregon State and Virginia Tech describe this tree as deciduous. PFAF instead calls it evergreen. Fall leaves turn yellow in shade. Sun-grown leaves may also show orange, red, and purple. Small green-white flowers grow in clusters from May to June. Insects pollinate them, and bees visit the flowers. Round drupes ripen to purple-black and hold yellowish flesh. PFAF places seed ripening in October.

Cascara grows in sun or shade. It does best in moist soil that drains well. It accepts sandy, loamy, and clay soils. It also tolerates mildly acid through mildly alkaline conditions. Oregon State lists hardiness to USDA Zone 3b. PFAF reports survival to at least 5°F [−15°C]. Garden uses include ornamental hedges and planting for wildlife. The bark yields green dye. Its light, soft wood has served for small tool handles.

The bark has a history of use as a laxative. This does not make fresh bark safe to use. PFAF warns of vomiting, cramps, and severe or bloody diarrhoea. Sources disagree about whether people can eat the fruit. Virginia Tech calls it inedible and notes its laxative effects. PFAF records food uses but also warns of possible toxicity. These conflicting accounts do not support treating it as safe food.