1. Berberis L. (barberry)

Plants shrubs. Stems with the leaves mostly replaced by spines, the normal foliage leaves clustered on very short shoots in the axils of the spines. Leaves many per plant, simple and unlobed, pinnately veined. Inflorescences axillary racemes or umbels, or flowers rarely solitary in leaf axils. Flowers with 3 small bractlets immediately below the calyx. Sepals 6, 3–5 mm long, petaloid, yellow. Petals 6, 2.5–3.0 mm long, yellow, bearing nectaries. Stamens 6, the anthers attached at the middle, opening by 2 apical flaps. Fruits berries. Seeds 4–6 mm long, narrowly to broadly ovoid, the seed coat hard, tan or more commonly reddish brown to black. About 500 species, North America, Europe, Asia, and the mountains of South America and east Africa.

The Missouri species of Berberis are deciduous shrubs with spiny stems, simple leaves, lax inflorescences, and red berries, but many species from other parts of the world are quite different. One such species, B. aquifolium Pursh (Mahonia aquifolium (Pursh) Nutt.), is widely grown as an ornamental in Missouri under the name Oregon grape. It is an unbranched evergreen shrub with spineless stems, pinnately compound leaves with spiny hollylike leaflets, dense racemes 3–11 cm long with 30–60 flowers, and glaucous blue berries. It has been reported to escape from cultivation occasionally in Michigan and eastern Canada, and it might be capable of persisting outside of cultivation in Missouri, at least briefly.

Many species of Berberis are grown as ornamental shrubs. However, some species serve as the alternate host for Puccinia graminis Pers., the fungus that causes black stem rust of wheat and other grain crops. Puccinia graminis has a two-phase life cycle, with the dikaryotic (telial and uredinial) stage attacking grains and wild grasses and the homokaryotic (aecial) stage attacking some species of Berberis (Alexopoulos et al., 1996). The fungus can overwinter on grasses only in areas with mild winters, but it overwinters on Berberis species even in very cold climates, so the presence of susceptible Berberis species can greatly increase losses from this fungus in nearby grain fields. Farming is only affected when susceptible barberries grow in open areas adjacent to grain fields; plants in wooded areas or areas remote from farmland have no significant impact on crops. The sale, transport, or cultivation of susceptible or untested species of Berberis is now banned by state and federal quarantine regulations, and extensive eradication programs have almost eliminated susceptible barberries (primarily B. vulgaris) in many areas where they once grew (Fulling, 1943; Roelfs, 1982). Because of this, barberries no longer affect grain growing in the United States, but quarantine laws are still enforced in order to prevent susceptible species from becoming reestablished in farming areas in the future (Roelfs, 1982).

Aside from the berries of some species, barberry plants are variously considered poisonous. Decoctions of a few species were used by Native Americans to treat sore throats, infected gums, jaundice, and diarrhea (Moerman, 1998).