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A genus of deciduous and evergreen shrubs, now including nearly two hundred species. The hardy ones are natives of Europe, N. Asia, and the two Americas; the common barberry (B. vulgaris) extends to N. Africa – perhaps introduced. The leading characteristics of the genus are, the yellow wood, yellow flowers, and the three-parted character of the flowers; the sepals being six or nine, the petals six, and the stamens six. The fruit is an oblong or egg-shaped berry containing one to several seeds. The stamens are irritable, and if touched at the base with a fine-pointed instrument like a pin, they suddenly move from their sheltered position in the concavity of the petals, and close inwards on the pistil. The object of this interesting power is, no doubt, to secure cross-fertilisation. An insect in search of honey pushes itself or its proboscis into the flower, sets the stamens in action, and, becoming itself smeared with pollen grains, carries them away to another flower and deposits them on the pistil.
The morphology of the leaves and spines of barberry is interesting. In the true barberry group, the 'leaf', as we call it, is really the terminal leaflet of a pinnate leaf, the side ones of which are suppressed, and the tuft of leaves as a whole is a branch in which the internodes are suppressed. Then the spine (usually three-parted, but sometimes simple, sometimes much divided), in the axil of which the tuft of leaves is borne, is a metamorphosed pinnate leaf. An occasional reversion to the ancestral type reveals their true origin.
As ornamental shrubs the barberries have many good qualities and several of them are in the very first rank of garden plants. They prefer a warm, loamy soil, but are by no means fastidious. Seeds are, as a rule, freely borne, and afford the best and readiest means of propagation; but for those sorts which do not produce seed in this country, and for those also that do not come true from seed like the coloured-leaved varieties, cuttings, layers, or division of the plants must be resorted to. Cuttings should be made of fairly ripened wood, and put in sandy soil under a bell-glass or in cold frames.
The following is a selection of species and hybrids usually available in commerce:
Evergreen or semi-evergreen: B. calliantha; candidula; darwinii; gagnepainii; hookeri; julianae (or sargentiana); linearifolia (slightly tender); pruinosa; × stenophylla (the clones listed and also 'Autumnalis'); valdiviana; verruculosa.
Deciduous or nearly so: B. × carminea (clones listed); dictyophylla; jamesiana; montana; × ottawensis 'Superba'; × rubrostilla (clones listed); 'Sibbertoft Coral'; temolaica; thunbergii and cvs; wilsoniae and vars.
The major work on the genus is Berberis and Mahonia by L. W. A. Ahrendt, published as Vol. 57 (No. 369) of The Journal of the Linnean Society (Botany), 1961.
The yellow wood of the barberries is due to the presence of a substance that has been used in dyeing, and exists even in the roots. The mature bark may be either reddish or a dull yellow.
The petals each have a pair of nectaries at the base and are sometimes termed honey-leaves. The pollination mechanism mentioned is as likely to result in self-pollination as in cross-fertilisation, especially if the visitor is a bumble-bee. In the absence of insect visitors, self-pollination occurs, since the anthers usually touch the stigma as the flower withers. The barberries are self-fertile, so good crops of berries are produced even by isolated plants.
The development of seedlings shows clearly the true nature of the barberry leaf. The pair of seed-leaves are followed by what is clearly a single leaflet, borne at the end of a wiry rachis and demarcated from it by a joint. The first leaves of a mahonia seedling are similar, but in that genus lateral leaflets are produced by those that follow and at the same time the rachis becomes stouter, while in Berberis successive leaves have an ever shorter rachis until the adult state is reached.
Spines appear at the nodes quite early in the development of the plant. A few species are virtually unarmed, bearing normal leaves at the nodes in place of spines, though these are not entirely absent. Conversely, normal leaves may be produced at the nodes in species that are mainly armed. After the juvenile phase is over, intermediate structures are uncommon, except in some South American species.
With regard to propagation, it is unfortunate that cuttings of some species, mostly deciduous, do not strike readily, if at all. As a result, many excellent species such as the South American B. chillanensis have become scarce in commerce or unobtainable. Grafting is sometimes resorted to, using seedlings of the purple forms of B. vulgaris or B. × ottawensis as stock, in order to make it easier for the purchaser to distinguish the suckers, which are all too freely produced by such plants. Raising from seed is easy, and more reliable than might be supposed, for it is only when related species are grown close together that the danger of cross-fertilisation arises.
The selection given on page 369 is still valid, but B. manipurana and B. × lologensis 'Stapehill' (see this supplement) might be added to the list of evergreens, together with B. coxii (page 378) and B. panlanensis (page 399 and this supplement).
A badly needed revision of the Old World species is now under way at the Royal Botanic Garden, Edinburgh. The first instalment is a synopsis of the section Wallichianae by D. F. Chamberlain and the Chinese botanist C. M. Hu, published in Notes Roy. Bot. Gard. Edinb., Vol. 42 (3), pp. 529-57 (1985). This section, whose type is the little known B. wallichiana, described from Nepal, comprises all the east Asiatic species with evergreen foliage, a fascicled inflorescence (sometimes reduced to a solitary flower) and purple or black, often pruinose, fruits, and is represented in cultivation by such species as B. candidula, B. gagnepainii and B. sargentiana. The new synopsis, with its excellent keys, is a great improvement on Dr Ahrendt's treatment, though nearly all the species that he recognised are upheld.