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A well-marked genus of evergreen and deciduous shrubs or small trees, confined to N. America. They are peculiarly characteristic of the Pacific coast region, where they constitute a large part of that 'almost impenetrably dense brushwood called “chapparal”, which covers the middle elevations of the coast range, and forms a distinct belt between the herbaceous vegetation of the foot-hills and the forest growth of the highest ridges and summits' (Greene). The flowers, usually of some shade of blue or white, are individually quite small, but they are so plentifully borne in a crowd of fascicles or umbels, that they form as a whole a dense and often showy panicle. Sepals and petals five, the latter of hooded form, narrowing at the base to a slender stalk. The leaves afford useful distinguishing characters: one group has them opposite, the other alternate; and the species of the latter group are again divisible according to the veining, some having three more or less prominent veins, and some being pinnate- or feather-veined.
The ceanothuses generally are somewhat tender, and, except where noted, should be given the protection of a wall. They are, however, fast-growing and flower well when young, so the loss of a mature plant is not an irreparable tragedy. Most are easily multiplied by cuttings put in during July and August in gentle heat and, where facilities are available, it is a good practice, with these and many other easily struck, borderline shrubs, to take precautionary cuttings each summer. With these reserves to fall back on, the gardener can afford to be more adventurous and make better use of the spells of mild or average winters.
The evergreen species and hybrids, when trained on a wall, should be pruned after flowering by shortening the laterals to within two or three buds of last year's stems; strong growths not needed for extending the framework should be cut back. See also C. × delilianus.
The standard work on the genus is: M. Van Rensselaer and H. E. McMinn, Ceanothus, published by the Santa Barbara Botanic Garden, California (1942). This admirable study is unfortunately no longer in print but the Californian species are treated in: H. E. McMinn, An Illustrated Manual of California Shrubs (1951), and P. A. Munz, A California Flora (1959).
A valuable survey of the California species by Michael Nevin Smith was published in Pacific Horticulture, Vol. 40(2), pp. 37-45 and Vol. 40(3), pp. 36-43 and 52-9 (1979).