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:

General Information

Mahonia oiwakensis is an evergreen shrub with erect stems; it usually grows 2.5 - 3.5 metres tall[]. Old plants in the wild have been known to reach a height of 12 metres, their erect trunk and stems each carrying a tuft of foliage at the summit[].
The plant is harvested from the wild for local use as a food and a medicine. It is often cultivated as an ornamental in gardens[].
Natural regeneration of this species is reported to be poor and no conservation or protection measures are in place. The plant is classified as 'Vulnerable' in the IUCN Red List of Threatened Species(2013)[].
The plant has escaped from cultivation in New South Wales and has become established in several sites. It has been assessed as a very high weed risk in New South Wales, where the priority is to prevent its establishment as an invasive weed in north-east NSW[].

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

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Range

E. Asia - southern China (Sichuan, Yunnan, Xizang), Taiwan
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Habitat

Broad-leaved forests, thickets, forest margins, slopes; at elevations from 600 - 3,800 metres[].

Properties

Weed Potential	Yes
Conservation Status	Vulnerable
Edibility Rating
Medicinal Rating
Habit	Evergreen Shrub
Height	5.00 m
Growth Rate	Medium
Pollinators	Insects
Cultivation Status	Ornamental, Wild

Cultivation Details

Mahonia oiwakensis is native to the waem temperate zone of southern China. It can tolerate occasional temperatures down to about -10°c when it is fully dormant[], though young growth in the spring is more sensitive and can be damaged at temperatures around 0°c[].
Succeeds in any good garden soil. Grows well in heavy clay soils. Dislikes windy positions, the plants can be badly damaged by cold drying winds[]. Prefers a shady sheltered position, growing well in woodland according to one report whilst another says that it requires a warm sunny sheltered position.
The flowers are fragrant[].
There is some confusion over the flowering and fruiting times of this species, I have seen some plants flowering in mid to late spring, whilst others have flowered in the winter and ripen their fruit in late spring to early summer - more research needs to be carried out in order to check if more than one species is grown under this name[].
Very tolerant of pruning, it can be cut right back into old wood if it has outgrown its welcome[].
Hybridizes freely with other members of this genus.
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[]. We have no data on susceptibility for this species[].

Edible Uses

Fruit - raw or cooked. The oval fruit is about 5 - 10mm long, it is quite juicy and has a nice acid flavour that children tend to love though many adults are less sure. The fruit is especially nice when added to muesli or porridge[]. Unfortunately, there is often relatively little flesh and a lot of seeds, though plants often also produce seedless fruits[]. Unlike many members of this species, the seedless fruits of this plant do not have a bitter flavour[].

Medicinal

In trials, an ethanol extract of the roots and stems has been shown to be antiinflammatory, apoptotic, hepatoprotective, analgesic and antimicrobial[].
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[].

Other Uses

None known

Propagation

Seed - best sown as soon as it is ripe in a greenhouse[]. 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 the greenhouse for at least their first winter. Plant them out in late spring or early summer and consider giving them some protection from the cold for their next winter.
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.