General: trailing and widely stoloniferous and stiff-branched woody shrub 10-30 cm tall. Bud scales in the flower cluster 3-8 mm long, mostly dropped soon.
Leaves: alternate, pinnate, the 5-7 leaflets oblong to ovate or ovate-lanceolate, 3-8 cm long, 2-5 cm broad, less than twice as long as broad, with mostly 15-43 prominent to small spine-tipped teeth, the upper surface glossy or dull, the lower surface always dull and more or less waxy-coated in appearance, covered with minute bumps visible only under at least 15x magnification.
Flowers: yellow, several in clusters 3-8 cm long. The 3 bractlets (or outer sepals) somewhat greenish, 2-3 mm long. The 3 inner sepals 6-8 mm long, bright yellow, slightly longer than the 6 oblong, 2-lobed petals. The 6 filaments usually with 2 short, more or less spreading teeth at the tip just below the anthers.
Fruits: berries, deep blue, round-ellipsoid, 7-14 mm long, covered with waxy coating.
Lower foothills to forested slopes, in w., c. and s.e. parts of MT. Also from OR and e. WA to Alberta and s. to SD, TX, NM, UT, s. NV, and n.e. CA.
The fruit of Oregon grape is edible raw or cooked. It has an acid flavor but it is rather nice raw, especially when added to muesli or porridge. Unfortunately, there is relatively little flesh and a lot of seeds. They are used for making jams. jellies etc. They can also be made into a refreshing lemonade-like beverage. When sugar is added, the fruit juice is similar to grape juice.
The root and root bark have agents that are pain-relieving, antiseptic, laxative, fever-reducing, tonic, that gradually restore health, increase bile flow to the intestines, tend to purify and cleanse the blood, induce urination, and that induce the removal (coughing up) of mucous secretions from the lungs. It improves the digestion and absorption and is taken internally in the treatment of coughs, fevers, psoriasis, syphilis, hemorrhages, stomach complaints, kidney problems and impure blood conditions. Externally, it is used as an antiseptic and healing wash or poultice on wounds and rheumatic joints. The roots are harvested in late autumn or early spring and dried for later use. A poultice of the fresh berries has been applied to boils. Berberine, universally present in rhizomes of Mahonia species, has marked antibacterial effects and is used as a bitter tonic. Since it is not appreciably absorbed by the body, it is used orally in the treatment of various enteric infections, especially bacterial dysentery. It should not be used with Glycyrrhiza species (Liquorice) because this nullifies the effects of the berberine. Berberine has also shown antitumor activity. The root and root bark are best harvested in the autumn.
Barberry, goldenseal, oregon grape and other plants containing berberine should be avoided during pregnancy and breastfeeding. They should be avoided if one has an over-active thyroid gland. High doses cause vomiting, lowered blood pressure, reduced heart rate, lethargy, nose bleed, skin & eye irritation and kidney infection.
A yellow dye is obtained from the inner bark of the stem and roots. It is green. Dark green, violet and dark blue-purple dyes are obtained from the fruit. A green dye is obtained from the leaves. Plants form suckers freely, making a good dense ground cover, though they can be slow to become established and will need weeding for their first few years after planting out. The sub-species M. repens rotundifolia has been especially recommended. A useful plant for preventing soil erosion on slopes.
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