This evergreen shrub, one of the most popular ceanothuses in gardens, has by some authorities been regarded as a variety merely of C. papillosus. The leaves are alternate, 1⁄5 to 1⁄2 in. long (rarely as much as 1 in.), elliptic to narrowly oblong or linear, the margins decurved and set with gland-tipped teeth; the upper surface is dark, shiny green, and rather resinous; the under-surface covered with a close grey felt; venation pinnate. Flowers of a bright blue, in roundish clusters on short peduncles. From C. papillosus it differs in the absence of the warty excrescences on the leaves to which that species owes its name, and in its smaller leaves. But in the Redwood zone of the Santa Cruz Mountains, where the ranges of the two species overlap, intermediate forms are found. C. dentatus makes a charming wall plant, and in the milder counties is hardy in the open ground. The hybrid C. × lobbianus (q.v. under C. thyrsiflorus) is sometimes cultivated as “dentatus”, but may be distinguished by its distinctly three-nerved leaves.
var. floribundus (Hook.) Trel. C. floribundus Hook. – Leaves usually broader and less revolute than in the type, and with scarcely glandular margins. Flowers borne in denser clusters on shorter peduncles. Such forms are reported to occur wild with the type.
In describing this variety, Trelease identified it with the C. floribundus of Hooker, a mysterious plant figured in the Botanical Magazine, t. 4806. It was raised at Veitch's nursery, Exeter, from seed collected by William Lobb in California around 1850, but exactly where is not known. From the gardener's point of view, this plant was distinguished not so much by its botanical characters as by the colouring of its flowers, which were of a particularly vivid shade of mazarine-blue. Not all plants falling botanically within the definition of Trelease's var. floribundus would have this quality and indeed most plants grown under this name are said to be ordinary C. dentatus (E. E. Kemp in Gard. Chron., 24th Aug. 1935). Others grown under this name are not forms of C. dentatus but C. × veitchianus. Whether any vegetative offspring of the Veitchian plant still exist is not certain.
The “C. microphyllus” of British gardens is a small-leaved form of C. dentatus. The true C. microphyllus Michx. is a dwarf, heath-like shrub with white flowers, found in the sand-barrens and pine-woods of the south-eastern U.S.A.