Oregon-grape - Mahonia Sp.

Family: Berberidaceae - Barberry Family

Berberis
"Habit: Shrub, generally rhizomed. Stem: spreading to erect, branched, spiny or not, vine-like or not; inner bark, wood generally bright yellow; over-wintering bud scales deciduous or not. Leaf: simple or pinnately compound, cauline, alternate, generally leathery, generally persistent; leaflets generally 3--11, +- round to lanceolate, generally spine-toothed. Inflorescence: raceme, axillary or terminal. Flower: sepals 9 in 3 whorls of 3; petals 6 in 2 whorls of 3, bases generally glandular; stamens 6; ovules 2--9, stigma +- spheric. Fruit: berry, spheric to elliptic, generally purple-black.
Species In Genus: +- 600 species: temperate worldwide. Etymology: (Latin: ancient Arabic name for barberry) Toxicity: Roots often TOXIC: spines may inject fungal spores into skin. Note: Contact with filament causes stamen to snap inward, possibly to deposit pollen on pollinator." ^[Jepson]

"Some authors regard the compound-leaved species as a separate genus, Mahonia. There are no consistent differences between the two groups other than the compound leaves, and studies suggest that the simple-leaved group is very likely polyphyletic.[1][4][5][6]" ^[Wiki-1]

Taxonomic Key to Mahonia

1. Leaflets usually 9-19, palmately nerved.....................................M. nervosa

1. Leaflets usually 3-11, pinnately nerved

2. Leaves more than twice as long as broad, mostly with 12-29 prominent spiny teeth; leaflets 5-11; plants 0.5-4.5 m tall.......................M. aquifolium

2. Leaves less than twice as long as broad, with 15-43 inconspicuous, spiny teeth; leaflets 3-7; plant 0.1--.6 m tall.........................M. repens

^[E-flora]

Mahonia contains 45 accepted, 61 synonym, and 46 unassessed species. ^{[ThePlantList]}

Local Species;

1. Mahonia aquifolium - Tall Oregon-grape ^{[E-flora][PCBC][TSFTK]}
2. Mahonia nervosa - Dull Oregon-grape ^{[E-flora][PCBC][TSFTK]}
3. Mahonia repens - Creeping Oregon-grape ^{[E-flora][TSFTK]}

Tall Oregon-grape - Mahonia aquifolium
Synonyms: Berberis aquifolium Pursh [E-flora-2][Turner, Kuhnlein][PFAF] Berberis aquifolium var. aquifolium [E-flora-2] Berberis fascicularis. [PFAF] Berberis piperiana (Abrams) McMinn [E-flora-2] Mahonia piperiana Abrams [E-flora-2] Odostemon aquifolium (Pursh) Rydb. [E-flora-2][PFAF] General: Evergreen shrub from a rhizome; stems branched, stoloniferous to stiffly erect, 0.5-2.5 (4.5) m tall; bark and wood yellowish. [IFBC-E-flora-2] Leaves: Evergreen, hollylike, alternate, pinnate; leaflets usually 5-11, pinnately nerved, more than twice as long as broad, mostly with 12-29 prominent spiny teeth, shiny above but less so beneath. [IFBC-E-flora-2] Flowers: Inflorescence of clustered racemes 3-8 cm long; flowers yellow, the segments in 6's. [IFBC-E-flora-2] Fruits: Clustered berries 7-14 mm in diameter, blue, glaucous, with a few large seeds, edible. [IFBC-E-flora-2] Habitat/Range: Mesic to dry open or closed forests in the lowland, steppe and montane zones; common in S BC; E to AB and S to ID and OR. [IFBC-E-flora-2] Status: Native [E-flora-2] Ecological Indicator Information "A shade-tolerant/intolerant, submontane to montane, Western North American evergreen shrub distributed more in the Cordilleran than the Pacific region. Occurs predominantly in continental cool temperate and cool semiarid climates on very dry to moderately dry, nitrogen-medium soils; its occurrence increases with increasing summer drought and continentality. Sporadic in summer-dry mesothermal climates, common in open-canopy Douglas-fir forests in the coast-interior ecotone. Often associated with Agropyron spicatum, Calamagrostis rubescens, and Rhytidiadelphus triquetrus. Characteristic of moisture-deficient sites." [IPBC-E-flora-2]

Dull Oregon-grape - Mahonia nervosa
"Mahonia nervosa is an evergreen Shrub growing to 0.6 m (2ft) by 1 m (3ft 3in) at a slow rate. It is hardy to zone (UK) 6. It is in leaf 12-Jan It is in flower from Feb to April. The flowers are hermaphrodite (have both male and female organs) and are pollinated by Insects. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils and can grow in heavy clay and nutritionally poor soils. Suitable pH: acid, neutral and basic (alkaline) soils. It can grow in full shade (deep woodland) semi-shade (light woodland) or no shade. It prefers dry or moist soil." [PFAF-1] General: Evergreen shrub from a rhizome; stems branched, erect, 10-60 cm tall, leafy; bark and wood yellowish. [IFBC-E-flora-1] Leaves: Evergreen, hollylike, turning reddish in the fall, alternate, pinnate; leaflets 9-19, palmately nerved, with spiny teeth. [IFBC-E-flora-1] Flowers: Inflorescence of clustered racemes up to 20 cm long; flowers yellow, the segments in 6's. [IFBC-E-flora-1] Fruits: Clustered berries 8-11 mm in diameter, blue, glaucous, with a few large seeds, edible. [IFBC-E-flora-1] Habitat / Range: Mesic to dry open slopes and open forests in the lowland, steppe and montane zones; common in SW BC, infrequent eastward in S BC; S to CA. [IFBC-E-flora-1] Origin Status: Native [E-flora-1] USDA Flower Colour: Yellow USDA Blooming Period: Mid spring USDA Fruit/Seed characteristics: Colour: Blue. Present from Spring to Summer [USDA-E-flora-1] Ecological Indicator Information "A shade-tolerant/intolerant, submontane to montane, Pacific North American evergreen shrub. Occurs in maritime to submaritime cool mesothermal climates on moderately dry to fresh, nitrogen-medium soils; its occurrence decreases with increasing precipitation, elevation, and continentality. Scatered to abundant, occasion­ally dominant, in the understory of semi-open forests (persists on cutover sites) on water-shedding sites. Inhabits coarse-skeletal soils. Commonly associated with Gaultheria shallon, Kindbergia oregana, and Polystichum munitum. Characteristic of mesothermal forests." Indicator Plants of Coastal British Columbia (Information applies to coastal locations only)[E-flora-1]

Species mentioned:

Barberry, Mahonia (Berberis) ^[EUCp] Mahonia nervosa, aquifolium, repens, fremontii ^[Berries] Mahonia aquifolium, M. nervosa var. nervosa ^{[Meuninck EWPUH]}

Hazards

• M. aquifolium:Barberry, goldenseal, oregon grape and other plants containing Berberine should be avoided during pregnancy and breastfeeding. Avoid if over active thyroid gland. High doses cause vomiting, lowered blood pressure, reduced heart rate, lethargy, nose bleed, skin & eye irritation and kidney infection. Liquorice as Glycyrrhiza species nullify berberine effects [301].^[PFAF-2]
• Root: The root is a potent medicine and can be TOXIC. ^[Berries]
• M. aquifolium: Berberine and other Berberis alkaloids were reported to be toxic to seedlings of dog rose and horse chestnut, causing atrophy. ^{[Leung ENCI]}
• Pregnancy: Do not use during pregnancy. ^{[CBMed][Meuninck EWPUH]}
  • M. aquifolium:White and Mavor preclude use in children under 1 year old, or during pregnancy (WAM). Canada requires bilingual warning against use during pregnancy (AHP). ^[PDR]
• M. aquifolium: "If Barney is right in saying that "goldenseal should not be taken for long periods of time," I suspect that the same would be true for those herbs containing similar compounds, such as barberry, goldthread, oregon grape, and yellow root (Barney, 1996). Therefore, I have lowered their safety ratings to one +. "Large doses of berberine can cause fatal poisoning” (CRC)." ^[PDR]
• M. aquifolium: "Not allowed as a non-medicinal ingredient in oral use products in Canada" (Michols, 1995). ^[PDR]
• M. aquifolium: "Hazards and/or side effects not known for proper therapeutic dosages" (PH2). ^[PDR]

Uses

"Of the thirteen species now recognized scattered through the country, seven occur in the records of the early uses of plants. The fruits of most were used by both the Indians and the early settlers to make a pleasantly acid drink. These berries were also used in making a tart preserve, and some of the Indian tribes dried the fruits for winter use. Probably the most important use for these plants, was in making a good yellow dye for baskets, buckskins, and fabrics." ^[EUCp]

Edible Uses

• Berries:
  • M. aquifolium and M. nervosa: Oregon grapes are edible but intensely bitter. ^[Berries] These berries, far from being poisonous, were, and perhaps still are, made into a very good jelly by the Oregonians. ^[EUCp] The berries were often combined with salal or some other berry as a sweetener. The mixture was boiled, mashed, dried and stored the mixture.^[Berries] The combined juices were also diluted with water and made into a refreshing drink.^[Berries]
  • M. aquifolium: Tart berries eaten in late summer. Native Americans smashed the berries and dried them for later use. They may be boiled with ample amounts of sugar into jam (or honey); the juice is tart. ^{[Meuninck EWPUH]} Very tart, but were eaten by many Indigenous groups. The berries were generally harvested in August, and were formerly eaten raw, but often only in small quantities. ^{[Turner, Kuhnlein]}
  • M. nervosa; Unfortunately, there is relatively little flesh and a lot of seeds. An acid flavour but it is rather nice raw, especially when added to muesli or porridge[K].^[PFAF-1]
    • M. nervosa; Preparation: "Raw or cooked[2, 3, 101]. Too acid for most tastes but they are very good in jams, jellies, pies etc[183]. They can also be used to enhance the flavour of bland fruits or made into a refreshing lemon-flavoured drink[183]." ^[PFAF-1]
• Leaves:
  • M. aquifolium: "Carrier Indians of the Northwest simmered young leaves and ate them. The smaller creeping M. nervosa prepared and eaten in the same way and is preferred but not as abundant." ^{[Meuninck EWPUH]}
  • M. nervosa; Young Tender Leaves - Cooked. Simmered in a small amount of water and eaten as a snack[183].^[PFAF-1]
• Flowers:
  • M. aquifolium: Flowers edible raw. They can also be used to make a lemonade-like drink. ^[EMNMPV.7]

Other Uses

The roots, and in some cases the sterns also, were crushed and boiled to obtain the color. The bark of both Berberis repens and Berberis pinnata was used as a laxative and to make a lotion to treat various skin diseases. From the roots a bitter tonic was made which served as a blood purifier. The leaves of B. repens were boiled and the tea taken to cure general aches and rheumatic pains. ^[EUCp]

• Berries:
  • M. aquifolium: The Karok Indians considered the berries to be poisonous, but pounded them, fresh, with the Bowers of Larkspur, Delphinium decorum, and salmon glue to make a paint for decorating bows and arrows. ^[EUCp]
• Dye: Native Americans not only gathered Mahonia species for medicinal uses, they also extracted a yellow dye that came from the berberine of the inner wood. It was the best dye for many things, and if Oregon grape did not grow locally, native peoples traded for it. They used the brilliant yellow dye for basketry materials, particularly beargrass (Xerophyllum tenax), and decorative ornaments such as porcupine quills. Yellow designs brightened buckskin clothing, moccasins, and ceremonial objects. Today, Oregon grape is used to dye rags for braided rugs.^[Berries]
  • M. aquifolium & M. nervosa: The shredded bark and roots of both species can also be simmered in water to make a bright-yellow dye. ^{[Meuninck EWPUH]}
• M. nervosa & M. aquifolium; "A yellow dye is obtained from the inner bark of the stem and roots[98, 101, 257]. Dark green, violet and dark blue-purple dyes are obtained from the fruit[168]. A green dye is obtained from the leaves [168]." ^[PFAF-1]
• Paint: The Karok of northern California believed the berries were poisonous but ingeniously pounded them fresh, with larkspur flowers and salmon glue, to make a durable purple paint for decorating bows and arrows. ^[Berries]

Medicinal Uses

Oregon grape was listed in the United States Pharmacopoeia from 1905 to 1916 and on the National Formulary from 1916 to 1937. Berberine salts are used in modern eyedrops and eye washes, and in Germany, tall Oregon grape bark extract is currently marketed for psoriasis. ^[Berries]
Native Americans steeped roots, stems, or bark for a tea-like infusion to use externally as a soothing wash to bathe sore eyes and as an antiseptic for skin sores. They mashed or chewed roots and stems, placing them on wounds to promote healing. Some tribes used the tea as an aperitif. ^[Berries]

• M. aquifolium: Oregon grape was often used by several native North American Indian tribes to treat loss of appetite and debility[254]. Its current herbal use is mainly in the treatment of gastritis and general digestive weakness, to stimulate the kidney and gallbladder function and to reduce catarrhal problems[254, 257]. Externally, it has been used as a gargle for sore throats and as a wash for blurry or bloodshot eyes[257].^[PFAF-2]
• M. aquifolium & M. nervosa; It improves the digestion and absorption and is taken internally in the treatment of psoriasis, syphilis, haemorrhages, stomach complaints and impure blood conditions. [4, 257]^[PFAF-1] [4, 238]^[PFAF-2]
• M. aquifolium: Used as an ingredient in certain tonic preparations. ^{[Leung ENCI]}
• Dosages: 0.5 tsp root bark/cup water 1 x/day (APA); 2 g root bark (HHB); 1-2 ml liquid root extract (APA; PNC); 10-20 drops fluid extract/3-4 hours (FEL); 0.3-1.5 g fluid extract (MAD); 0.6-3.75 g tincture (MAD). ^{[HMH Duke]}
• Berries:
  • M. aquifolium:
    • Unfortunately, there is relatively little flesh and a lot of seeds. An acid flavour but it is rather nice raw, especially when added to muesli or porridge[K].^[PFAF-2]
    • M. aquifolium; "One Saanich woman said that the berries were eaten as an antidote to shellfish poisoning". ^{[Turner&Kuhnlein]}
    • Harvesting: If you don't want to dig the roots up, then just collect a bunch of the grapelike fruits in autumn. ^{[Davies HNHN]}
    • Preparation: "Fruit - raw or cooked[2, 3, 5, 95]. The fruit is almost as large as a blackcurrant and is produced in large bunches so it is easy to harvest[K]. Unfortunately, there is relatively little flesh and a lot of seeds, though some plants have larger and juicier fruits[K]. The cooked fruit tastes somewhat like blackcurrants[K]. The fruit can also be dried and stored for later use[257]." ^[PFAF-2]
    • Preservation: Stored, either by covering them fresh with straw and leaves, or by squeezing and mashing them in baskets and spreading them out to dry in cakes. Sometimes boiled to a jam-like consistency and made into juice, which was heated and drunk. Often the berries were mixed with other, sweeter fruits, such as salal on the Coast or saskatoons in the Interior. Nowadays, people make jam or jelly from the berries, or jar them. [Turner, Kuhnlein]
  • M. nervosa; The fruit is an excellent safe and gentle laxative [257].^[PFAF-1]
• Root & Bark: Root and bark decoctions used to treat multiple ailments. Popular as a tonic and blood purifier.^[Berries]
  • M. aquifolium:"The medicinal parts are the dried rhizome and the roots, the dried branch and twig bark, as well as the root bark." [PDR]
  • M. aquifolium: In Bulgaria, the stem bark and roots are used to treat arthritis and chronic inflammatory conditions of the kidneys, liver, and gallbaldder. ^{[Leung ENCI]}
• Root:
  • M. aquifolium: Root is used for the treatment of acne and psoriasis.^[BMBBed]
    • Harvesting: ''M. aquifolium:' The root and root bark are best harvested in the autumn[213]. The roots are harvested in late autumn or early spring and dried for later use[238]. ^[PFAF-2]
    • M. aquifolium: fresh root tincture, 20-30% (IM (inflammation- modulating), AM (antimicrobial), AC (anti- comedogenic), bitter) ^[CBMed]
  • M. nervosa; A decoction of the peeled and chopped root bark has been used as a wash in treating arthritis and as an eyewash for red itchy eyes[257]. ^[PFAF-1]
    • M. nervosa; The root and root bark are best harvested in the autumn[213]. ^[PFAF-1]
• Eyewash:
  • M. aquifolium & M. nervosa : The bark infusion was used by Native Americans as an eyewash.^{[Meuninck EWPUH]}

Lore

The Navajo used Mahonia sp. to cure scorpion bite and remove bad luck.^[Berries]

According to the Doctrine of Signatures-a belief that a plant's physical characteristics hinted at what disease it was good for- the yellow flowers and yellow wood indicated usefulness for treating jaundice and gallstones. A syrup of berries was given for dysentery and fevers.^[Berries]

"In northern California and vicinity, the Karok used...Mahonia aquifolium, M. oreganos,... as poisons" ^{[David E. Jones]}

Phytochemistry

• Alkaloids:
  • M. aquifolium:
    • Berberine ^[CRNAH][PDR] (benzyl isoquinoline type) [PDR]
    • berbamine ^{[Skidmore-Roth MHH]}
    • corytuberine ^{[Skidmore-Roth MHH]}
    • columbamine ^{[Skidmore-Roth MHH][CRNAH]}
    • isothebaine ^{[Skidmore-Roth MHH]}
    • isocorydine ^{[Skidmore-Roth MHH][PDR]} (aporphine type) [PDR]
    • magnoflorine ^[CRNAH]
    • oxyacanthine ^{[Skidmore-Roth MHH][PDR]} (bisbenzyl isoquinoline type) [PDR]
    • oxyberberine ^{[Skidmore-Roth MHH][CRNAH]}
    • protoberberine ^{[Skidmore-Roth MHH][CRNAH]}
    • Isoquinoline alkaloids (in the root bark, 7 to 16%, in the stem bark, 2.4-4.5%):

"Berberis spp. are rich inisoquinoline alkaloids; those in B. vulgaris include berberine, berbamine, oxyacanthine, jatrorrhizine, columbamine, palmatine, isotetrandine (berbamine methyl ether), bervulcine, and magnoflorine;¹ those in B. aquifolium include aromoline, obamegine, oxyberberine, berbamine, and oxyacanthine.²" ^{[Leung ENCI]}

Berberine

Roots, stems and leaves used medicinally for their berberine content. Berberine has antibiotic and analgesic properties.^[Berries]

Berberine Yields

Berberine yield among individual samples ranged from 0.03 % to 0.97 %. In both species, berberine yield was greatest in the lower root, and decreased moving up the plant. There was no significant difference in berberine yield between the two species at any particular plant.^[PWMP]

The season of harvest (fall or spring) had no effect on berberine yield. Likewise, there was no difference in the response between samples harvested in spring 2010 and spring 2011; while this could indicate that one-year storage does not affect berberine yield, it also may be interpreted to mean that year-to-year variation in berberine production is unlikely.^[PWMP]

Our findings show that M. nervosa may have equal value to M. aquifolium, despite the preference among buyers for the latter species. More analytical testing needs to be done to confirm this. For one thing, only berberine content was analyzed; however, Mahonia species contain many other alkaloids which may be contributing factors to their bioactivity and medicinal value (Brinker 2005; Suess and Stermitz 1981).^[PWMP]

Regeneration

The regeneration study suggests that selective harvest as opposed to complete removal of Oregon-grape plants within a given area allows for a more rapid rebound in plant cover and density. In practice, partial harvest may be more difficult to execute, since the roots of neighboring plants intermingle, causing the removal of one plant to disturb many others. Oregon-grape resprouts vigorously from root fragments, allowing for the population to regenerate following harvest. However, it is a slow-growing species, and our study did not examine how long it would take for the belowground material to regenerate to a level suitable for a second harvest.^[PWMP]

Pharmacology

• Root:
  • M. aquifolium: Root is Bitter, antimicrobial, liver stimulant ^[CBMed] The root and root bark is alterative, blood tonic, cholagogue, diuretic, laxative and tonic[4, 21, 165, 257]. ^[PFAF-2]
  • M. nervosa; Root - Alterative and tonic[4]. ^[PFAF-1]
• M. aquifolium & M. nervosa : When eaten raw in small amounts, the fruit is slightly emetic. ^{[Meuninck EWPUH]}
• M. aquifolium & M. nervosa : A decoction of stem used as an antiemetic. ^{[Meuninck EWPUH]}
• M. aquifolium & M. nervosa : The bitter drug may prove an appetite stimulant ^{[Meuninck EWPUH]}
• Berries M. aquifolium: The fruit is an excellent safe and gentle laxative [257].^[PFAF-2] Some people considered them to have "tonic" properties. ^{[Turner&Kuhnlein]}
• M. aquifolium: Three clinical studies (open-label) on psoriasis evaluated the effect of Mahonia aquifolium on psoriasis. 57 In a study where a cream containing the botanical (10%) was applied by thirty-nine patients for twelve weeks, a significant improvement in symptoms was observed and lasted for up to one month after the end of the treatment. ^{[Alachi IBM]}
• M. aquifolium: Oregon grape root: Besides displaying antimicrobial activity due to berberine and other constituents, Oregon grape root inhibits proinflammatory cytokines. A cream containing 10% Mahonia extract ("psorberine”)..., treated three times daily over a period of 12 weeks showed significant improvement of the Eczema Area and Severity Index (EASI) score (15)[LOE- B]. ^[BMBBed]

Cultivation

• M. aquifolium: "This species can be grown as a low hedge and 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 [197, 200]." ^[PFAF-2]
• M. nervosa; "An easily grown plant, it thrives in any good garden soil[11, 200] but also succeeds in poor dry ones. Another report says that it is best on a lime-free soil[182]. Grows well in heavy clay soils. Prefers a sunny position[3] but succeeds in heavy woodland shade[K]. Hybridizes freely with other members of this genus. Plants are growing and fruiting well at Wakehurst Place in Sussex, but they do not generally do well in Britain[11]. Resistant to honey fungus[88]."^[PFAF-1]

Propagation

M. nervosa; "Seed - best sown as soon as it is ripe in a cold frame[78]. It usually germinates in the spring[K]. '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[K]. 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^oc. 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[78]. 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[11]. Leaf cuttings in the autumn."^[PFAF-1]

Uses of Related Sp.

• "Low Oregon-grape (Berberis nervosa), a Pacific Coastal species found in shady woods west of the Cascades in southwestern British Columbia, south to California, was used within its range in the same way as tall Oregon-grape (Gunther, 1973; Turner, 1975, 1978; Galloway, 1982; Turner et al., unpubl. notes, 1987; Turner et al., 1990). Some Lower Nlaka'pamux people preferred it over the latter; others did not distinguish between the two species." ^{[Turner&Kuhnlein]}
• Different forms of Oregon grape have different uses. ^{[Skidmore-Roth MHH]}
• M. aquifolium: "Whenever you see barberry (Berberis) mentioned in a formula, mahonia will often do just as well. ^{[Davies HNHN]}

References

• E-flora
  • [1] Mahonia nervosa, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Mahonia%20nervosa&redblue=Both&lifeform=3 In Klinkenberg, Brian. (Editor) 2014. E-Flora BC: Electronic Atlas of the Plants of British Columbia [eflora.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. [Accessed: 12/30/2014]
  • [2] Mahonia aquifolium, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Mahonia%20aquifolium&redblue=Both&lifeform=3, Accessed Sept 11, 2016
  • [3] Mahonia repens, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Mahonia%20repens&redblue=Both&lifeform=3, Accessed Sept11, 2016
• [Jepson] Michael P. Williams 2016. Berberis, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?tid=8928, accessed on September 11, 2016.
• [ThePlantList] The Plant List - A working list of all plant species, Royal Botanical Gardens, http://www.theplantlist.org/1.1/browse/A/Berberidaceae/Mahonia/, Accessed June 18, 2014
• [PFAF] Plants For A Future
  • [1] Mahonia nervosa, http://www.pfaf.org/user/Plant.aspx?LatinName=Mahonia+nervosa, Accessed Dec 30, 2014
  • [2] Mahonia aquifolium, http://www.pfaf.org/user/plant.aspx?latinname=Mahonia+aquifolium, Accessed Sept 11, 2016
• [PWMP] The Potential for Mahonia nervosa as a Wildcrafted Medicinal Product in the Pacific Northwest, Amy T. Grotta, Oregon State University Extension Service, 505 N. Columbia River Hwy., St. Helens, OR 97051, USA, Published Online Feb 23, 2013, Economic Botany.
• [Wiki] Wikipedia
  • [1] https://en.wikipedia.org/wiki/Berberis, Accessed Sept 11, 2016
    • [1] Flora of North America, vol 3
    • [4] Loconte, H., & J. R. Estes. 1989. Phylogenetic systematics of Berberidaceae and Ranunculales (Magnoliidae). Systematic Botany 14:565-579.
    • [5] Marroquín, Jorge S., & Joseph E. Laferrière. 1997. Transfer of specific and infraspecific taxa from Mahonia to Berberis. Journal of the Arizona-Nevada Academy of Science 30(1):53-55.
    • [6] Laferrière, Joseph E. 1997. Transfer of specific and infraspecific taxa from Mahonia to Berberis. Bot. Zhurn. 82(9):96-99.