Mahonia dictyota, Mahonia amplectens, Mahonia pumila, and Mahonia wilcoxii are very similar, and the characters that separate them (height, glossiness and crispation of leaflets, and size and number of marginal teeth) are rather variable within the species. Mahonia piperiana also belongs to this group, although it is usually more distinct because of its thinner leaflets with more slender, more numerous marginal spines[
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[
Berberis amplectens (Eastw.) Wheeler
Mahonia amplectens is an evergreen shrub growing 20 - 120cm tall. The plant suckers to form a cluster of unbranched stems[
The plant can be harvested from the wild for local use as a food and a medicine.
The plant is restricted to the Peninsular Ranges of southern California and is of conservation concern[
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.
Southwestern N. America - California
Rocky slopes in chaparral and open forest; at elevations from 900 - 1,900 metres[
Species in this genus tend to be easily grown plants that thrive in any good garden soil, including heavy clays. They generally prefer a semi-shaded woodland position in a damp, slightly acid to neutral humus-rich soil[
Plants are generally very tolerant of pruning and can be cut right back into old wood if they have outgrown their welcome[
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 Puccinia graminis[
The dark blue, ovoid to elliptic fruits are 7 - 9 mm long, juicy and solid[
]. We have no specific information on edibility for the fruit of this species, but all members of the genus have more or less edible fruit[
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[
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.