Berberis aquifolium

Berberis aquifolium, the Oregon grape or holly-leaved barberry, is a species of flowering plant in the family Berberidaceae, native to western North America. It is an evergreen shrub growing 1-3 m tall and 1.5 m wide, with pinnate leaves consisting of spiny leaflets, and dense clusters of yellow flowers in early spring, followed by dark bluish-black berries.

The berries are included in the diet of some aboriginal peoples of the Pacific Northwest, and the species is recognized as the state flower of Oregon.

Description
Berberis aquifolium grows to 1–3 m tall by 1.5 m wide. The stems and twigs have a thickened, corky appearance. The leaves are pinnate and up to 30 cm long, comprising spiny leaflets. The leathery leaves resemble those of holly. The yellow flowers are borne in dense clusters 3–6 cm long in late spring. Each of the six stamens terminates in two spreading branches. The six yellow petals are enclosed by six yellow sepals. At the base of the flower are three greenish-yellow bracts, less than half as long as the sepals. The spherical berries are dark dusty-blue and tart in taste.

Chemistry
Berberis aquifolium contains 5'-methoxyhydnocarpin (5'-MHC), a multidrug resistance pump inhibitor, which works to decrease bacterial resistance in vitro.

Taxonomy
Some botanists continue to place part of the barberry genus Berberis in a separate genus, Mahonia. Under this classification Berberis aquifolium is named Mahonia aquifolium. As of 2023 Plants of the World Online (POWO) classifies it as Berberis aquifolium with no valid subspecies.

Etymology
The Latin specific epithet aquifolium denotes "sharp-leafed" (as in Ilex aquifolium, the common holly), referring to the spiny foliage.

Berberis aquifolium is not closely related to either the true holly (Ilex aquifolium) or the true grape (Vitis), but its common name, Oregon-grape holly comes from its resemblance to these plants.

Distribution and habitat
Berberis aquifolium is a native plant in the North American West from Southeast Alaska to Northern California to central New Mexico, often occurring in the understory of Douglas-fir forests (although other forest types contain the species) and in brushlands in the Cascades, Rockies, and northern Sierra Nevada.

Ecology


As with some other Berberis, Berberis aquifolium can serve as an alternate host for Wheat yellow rust (Puccinia striiformis f. sp. tritici; the primary host of Pst being wheat). However, in B. aquifolium this was only achieved by intentional inoculation in a lab, and it remains unknown whether this occurs naturally.

In some areas outside its native range, Berberis aquifolium has been classified as an invasive exotic species that may displace native vegetation.

Cultivation
Berberis aquifolium is a popular subject in shady or woodland plantings. It is valued for its striking foliage and flowers, which often appear before those of other shrubs. It is resistant to summer drought, tolerates poor soils, and does not create excessive leaf litter. Its berries attract birds.

Numerous cultivars and hybrids have been developed, of which the following have gained the Royal Horticultural Society's Award of Garden Merit:
 * M. × wagneri 'Pinnacle' (B. aquifolium × Berberis pinnata)
 * 'Apollo'

Uses
The small purplish-black fruits, which are quite tart and contain large seeds, are edible raw after the season's first frosts. They were included in small quantities in the traditional diets of Pacific Northwest indigenous peoples, mixed with salal or another sweeter fruit. Today, they are sometimes used to make jelly, alone or mixed with salal. Oregon-grape juice can be fermented to make wine, similar to European barberry wine folk traditions, although it requires an unusually high amount of sugar.

The inner bark of the larger stems and roots of Oregon grape yield a yellow dye. The berries contain a dye that can be purple, blue, pink, or green depending on the pH of water used to make the dye, due to the berries containing a naturally occurring pH indicator.

Medicinal uses
Some Indigenous peoples of the Northwest Plateau use Oregon grape for indigestion.

The plant contains berberine and reportedly has antimicrobial properties similar to those of goldenseal.

Culture
In 1899, Oregon-grape was recognized as the state flower of Oregon.