The genus Mahonia is not universally accepted. Many botanists prefer to treat it as part of Berberis - as per the Flora of N. America[]. However, although they are very closely related (and there are some intergeneric hybrids), from the point of view of the gardener they are quite distinct genera. We are therefore following the treatment in the Flora of China[] which treats them as distinct. There is, however, at least one major revision (of the Chinese genera) currently (2016) in preparation and we will review the position of Mahonia once we have seen that revision[].

Common Name: Oregon Grape

General Information

Mahonia aquifolium is an evergreen shrub usually growing 30 - 250cm tall, exceptionally reaching 450cm. The plant sends up a cluster of more or less unbranched stems from underground suckers[].
The plant is harvested from the wild for local use as a food and medicine. It has achieved a high reputation in the treatment of various skin conditions and is harvested from the wild in large quantities for use in making skin creams. The plant is also commonly grown as an ornamental, where selevated cultivars can be used for ground cover and hedges.
This species has been introduced into many areas as an ornamental. It escapes regularly from cultivation in private and public gardens to form spontaneous woody vegetation[]. Populations usually consist of distinct patches formed by one or more genets, but the shrub can sometimes cover the entire understorey. It can out-compete native species due to its successful reproductive strategy, i.e. the colonization of available space due to repeated recruitment of seedlings[].

Known Hazards

All parts of the plant contain the alkaloid berberine - this is most concentrated in the roots, stems and inner bark, and least concentrated in the fruits. In small quantities berberine has a range of effective medicinal applications but, in excess, can cause vomiting, lowered blood pressure, reduced heart rate, lethargy, and other ill-effects.
The fruit of most, if not all, members of this genus are more or less edible and can be eaten in quantity since the levels of berberine in the fruit are very low.

Botanical References

, ,

Range

Western N. America - British Colombia, Washington, Idaho, Montana, Oregon, northern California

Habitat

Mixed coniferous woods; at elevsations up to 2,000 metres. Open woods and shrublands; at elevations up to 2,100 metres[].

Properties

Weed Potential	Yes
Edibility Rating
Medicinal Rating
Habit	Evergreen Shrub
Height	2.00 m
Pollinators	Insects, Self
Self-fertile	Yes
Cultivation Status	Wild

Cultivation Details

Mahonia aquifolium is a very tolerant plant, capable of growing in a wide range ot temperate climates. Plants are hardy to about -20°c[].
A very easy plant to grow, thriving in any good garden soil, though preferring acid soils[, , ] It prefers semi-shade, but can tolerate full sun and dense shade under trees[, , ]. It grows well in heavy clay soils and also succeeds in dry soils if it is given a good mulch annually[]. It dislikes exposure to strong winds[].
Very tolerant of pruning, plants can be cut back into old wood if they grow too large and straggly[]. Spring is the best time to do this[].
Suckers are fairly freely produced, with established plants forming dense thickets[].
Most plants grown under this name are casual hybrids with Mahonia repens[]. This species is easily confused with Mahonia pinnata[], with which it also hybridizes[].
The flowers are delicately scented[]. A number of named forms have been developed for their ornamental value[].
This species is notably resistant to honey fungus[, ].
Some Berberis/Mahonia species (especially Berberis vulgaris) harbour the black stem-rust fungus (Puccinia graminis Persoon). This is a major disease of wheat and barley crops and can spread from infected barberries to the grain crop. The sale or transport of susceptible or untested species of Berberis is illegal in the United States and Canada[]. This species is resistant to infection by the fungus[].
This plant is the state flower of Oregon[].

Edible Uses

Fruit - raw or cooked[, , , ]. The fruit is almost as large as a blackcurrant and is produced in large bunches so it is easy to harvest[]. It has an acid flavour, but it is rather nice raw and is especially good when added to a porridge or muesli[]. Unfortunately, there is relatively little flesh and a lot of seeds, though some plants have larger and juicier fruits[]. The cooked fruit tastes somewhat like blackcurrants[]. The fruit can also be dried and stored for later use[].

Flowers - raw. They can also be used to make a lemonade-like drink[].

Medicinal

Oregon grape was often used by several native North American Indian tribes to treat loss of appetite and debility[]. It is still a popular remedy in modern herbalism, being used mainly in the treatment of gastritis and general digestive weakness, to stimulate liver, kidney and gallbladder function and to reduce catarrhal problems[, , ]. Extensive trials have shown that a cream containing the root or stem extract is a safe and effective treatment for psoriasis and other skin conditions.

The root and root bark are alterative, antibacterial, antioxidant, blood tonic, cholagogue, diuretic, laxative and tonic[, , , ]. It improves the digestion and absorption and is taken internally in the treatment of psoriasis, syphilis, haemorrhages, stomach complaints and impure blood conditions[, , ].
Externally, it is used in the form of a cream to treat skin conditions such as psoriasis, whilst a decoction has been used as a gargle for treating sore throats and as a wash for blurry or bloodshot eyes[].
The roots are harvested in late autumn or early spring and dried for later use[].

The fruit is an excellent gentle and safe laxative[].

In Germany, several studies have indicated that Mahonia aquifolium exerts anti-psoriasis activities though inhibiting antiinflammation and hyperproliferation of keratinocytes, and that alkaloids may be responsible for the anti-psoriasis activity of this plant[].
Mahonia species have a long history of medicinal usage, with several members of the genus being commonly used in traditional medicine and also in modern herbalism. They are employed in the treatment of a wide range of conditions and have, in particular, been demonstrated to exert good efficacy in the clinical treatment of dysentery, internal and external haemorrhage, acne vulgaris and chronic pharyngitis amongst other diseases. Phytochemical research into this genus has resulted in the identification of more than 150 chemical constituents, amongst which alkaloids are predominant. The isolated compounds and crude extracts have been shown to exhibit a wide spectrum of in vitro and in vivo pharmacological effects, including antimicrobial, anti-inflammatory, hepatoprotective, antioxidant, antimutagenic and analgesic properties[]
Berberine, an alkaloid that is universally present in the rhizomes and stems of Mahonia species, has been shown to have a marked antibacterial effect[] and is also used as a bitter tonic[]. Since it is not appreciably absorbed by the body, it can be used orally in the treatment of various enteric infections, especially bacterial dysentery[].
Berberine has also shown antitumour activity[].
The plant should not be used with Glycyrrhiza species (Liquorice) because this nullifies the effects of the berberine[].

Agroforestry Uses:

This species can be grown as a low hedge that does not need trimming.
Because of its suckering habit, it also makes a good dense ground cover plant though it can be slow to become established[, ].
The plant may be useful for erosion control It has a high tolerance of chemical pollutants and favourable root morphology, which mean that it could be used in urban landscaping and bioengineering; it also has a high abiotic tolerance[].

Other Uses

A yellow dye is obtained from the inner bark of the stem and roots[, , ]. It is green according to another report[].
Dark green, violet and dark blue-purple dyes are obtained from the fruit[].
A green dye is obtained from the leaves[].

Propagation

Seed - best sown as soon as it is ripe in a cold frame[]. It usually germinates in the spring[]. 'Green' seed (harvested when the embryo has fully developed but before the seed case has dried) should be sown as soon as it is harvested and germinates within 6 weeks[]. Stored seed should be sown as soon as possible in late winter or spring. 3 weeks cold stratification will improve its germination, which should take place in 3 - 6 months at 10°c. Prick out the seedlings when they are large enough to handle and grow them on in a cold frame for at least their first winter. Plant them out in late spring or early summer.
Division of suckers in spring[]. Whilst they can be placed direct into their permanent positions, better results are achieved if they are potted up and placed in a frame until established[].
Leaf cuttings in the autumn.