A densely branched evergreen shrub, usually low and spreading in the wild state but reaching 12 ft on a wall, with abundant foliage closely packed on short, stiff lateral branchlets. Leaves opposite, pinnate-veined, obovate to rounded in general outline, 1⁄8 to 1⁄2 in. long, wedge-shaped to rounded at the base, often truncate or retuse at the apex, dark glossy green above, minutely downy beneath, mostly toothed, at least near the apex, more rarely entire. Flowers bright blue to rich purplish blue, in sessile or short-stalked umbels. Bot. Mag., t. 4664.
Native of California, found only on the Monterey peninsula, whence it was introduced by Hartweg for The Royal Horticultural Society in 1847. In the last edition of this work two forms of this species were described. One, which matches Nuttall's type, was shown by Miss Willmott in 1915 and became known as the 'Warley variety'; it has rather rounded, scarcely toothed leaves and short-stalked umbels. The other, commoner in gardens at that time, was introduced by Lobb sometime between 1849 and 1857, when collecting for Veitch's nurseries: it has narrower leaves, toothed near the apex, longer-stalked umbels and flowers of a paler shade. This form was distinguished by Sprague as var. pallens, but appears to fall within the limits of variability of typical C. rigidus.
This is one of the most beautiful of ceanothuses but, unfortunately, is also one of the tenderest. Against a wall at Kew it grows and flowers well every season, but in very hard winters is injured or killed even with that protection. It has no chance at all in the open. Like some other species, it is not long-lived, and the stock should be renewed occasionally by means of cuttings. It flowers from April to June, and will reach a height of 12 ft on a wall.
The following is a closely related species and indeed is part of C. rigidus as understood by Jepson:
C. ramulosus (Greene) McMinn C. cuneatus var. ramulosus Greene – Leaves usually less crowded than in C. rigidus; branchlets arching and more flexible. Flowers paler, in shades of lavender, pale blue, or white. This species has a wide distribution in the Coast Range, while C. rigidus, as now understood, is confined to the Monterey peninsula. McMinn (Ceanothus, 1942) considers that some plants grown in Britain as C. rigidus or var. pallens really belong to this species.