Rubus ursinus is a North American species of blackberry or dewberry, known by the common names California blackberry, California dewberry, Douglas berry, Pacific blackberry, Pacific dewberry and trailing blackberry.

The plant is native to western North America, found in British Columbia (Canada); California, Idaho, Montana, Oregon, and Washington (Western U.S.); and Baja California state (Mexico).

Rubus ursinus is a wide, mounding shrub or vine, growing to 2–5 feet (0.61–1.52 m) high, and more than 6 feet (1.8 m) wide. The prickly branches can take root if they touch soil, thus enabling the plant to spread vegetatively and form larger clonal colonies. Leaves usually have 3 leaflets but sometimes 5 or only 1, and are deciduous. The plant is dioeocious, with male and female plants on separate plants, also unusual for the genus. As with other Rubus, the canes are typically vegetative the first year, and reproductive in the second. Flowers are white with narrower petals than most related species, and have a fragrance. The sweet, very aromatic, edible fruits are dark purple, dark red, or black and up to 2 centimeters (0.8 inches) in length.

Diverse wildlife eat the berries, including songbirds, deer, bear, and other large and small mammals. It is of notable pollinator and nesting material value for native bee and bumble bee species. This blackberry species is a larval food source for the western tiger swallowtail butterfly (Papilio rutulus), the mourning cloak butterfly (Nymphalis antiopa), the gray hairstreak butterfly (Strymon melinus), and the spring azure butterfly (Celastrina ladon). Native Americans, such as the Kumeyaay, Maidu, Pomo and Salish peoples, used Rubus ursinus as a fresh and dried fruit source and as a traditional medicinal plant.

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