A low, spreading, densely branched shrub attaining in time a height and width of about 5 ft. Leaves alternate, 1⁄4 to 1⁄2 in. long, elliptic to almost rounded, dark green and somewhat hairy above, deeply furrowed along the courses of the midrib and pinnately arranged veins; paler beneath, and hairy along the veins; margins revolute. Flowers deep blue in clusters about 1 in. long, borne in April and May.
A local species, confined to a few localities in the Californian counties of Santa Barbara and San Luis Obispo. It is closely related to C. dentatus but well distinguished by its impressed veins. Although described in 1888, this attractive species was not much cultivated until the Santa Barbara Botanic Garden recognised its merits and distributed it. It is one of the hardiest and most satisfactory of the evergreen species. Except in the milder parts it is best grown on a wall, where it may reach a height of 8 ft or even more.
var. nipomensis McMinn – Taller than the type (to 10 ft high), with lighter green, less furrowed and less revolute leaves.
C. (impressus × thyrsiflorus (?))'Burtonensis'. – A wild hybrid, believed to be of the parentage stated, of which a single plant was found on the Burton Mesa in 1941 and propagated in the Santa Barbara Botanic Garden; introduced to cultivation in Britain by F. P. Knight, Director of the R.H.S. Garden, in 1963. It appears to be very near to C. impressus but differs from the form of that species usually seen in cultivation in this country in its more rounded, often almost orbicular, glossy leaves. There is a specimen of this attractive ceanothus on the Laboratory wall in the R.H.S. Garden, Wisley.
From the Supplement (Vol. V)
† C. 'Puget Blue'. – Distributed as a cultivar of C. impressus, this differs, at least from the commonly cultivated clones of that species, in its larger leaves up to 1 in. long, with glandular, scarcely revolute margins. It is also more erect than these, attaining 6 ft in height in two seasons, and eventually making a large bush when allowed to grow freely. It was raised by Mr L. L. Edmunds of Danville, California, before 1945, and became widely grown in the Seattle area of Washington; in California it is too demanding of moisture to succeed. It received an Award of Merit when shown by the late Lord Talbot de Malahide in 1971.