Branchlets not spinose, leaves 3-ribbed. Leaves broad-ovate to elliptic, subcordate or rounded at base, pale and tomentose below.1. [C. arboreus] (G). Leaves elliptic, acute at base, glabrous except on the veins below.2. [C. thyrsiflorus] (G). Branchlets spinose; leaves with a single midrib, mostly elliptic, rounded or subcordate at base, glabrous.3. [C. spinosus] (G).
1. [Ceanothus arboreus] Greene.
Leaves broad-ovate or elliptic, acute, conspicuously glandular-crenate, dark green and softly puberulent on the upper surface, pale and densely tomentose on the lower surface, 2½′—4′ long and 1′—2½′ wide, with prominent veins; petioles stout, pubescent, ½′—1′ in length; stipules subulate from a broad triangular base, ¼′ long. Flowers pale blue opening in July and August, on slender hairy pedicels ½′—1′ long, from the axils of large scarious caducous bracts, in ample compound densely hoary-pubescent thyrsoid clusters 3′—4′ long and 1½′—2′ wide, on a leafy or naked axillary peduncle at the end of young branches. Fruit black, ¼′ across.
A round-headed tree, 20°—25° high, with a straight trunk 6′—10′ in diameter, dividing 4°—5° from the ground into many stout spreading branches, and slender slightly angled pale brown branchlets covered with short dense tomentum, becoming in their second season terete, nearly glabrous, roughened with scattered lenticels and marked by large elevated leaf-scars; often a shrub. Bark of the trunk dark brown, about ⅛′ thick, and broken into small square plates separating into thick scales.
Distribution. Santa Catalina, Santa Cruz, and Santa Rosa Islands of the Santa Barbara group off the coast of southern California; most abundant and of its largest size on the northern slopes of Santa Cruz; on the other islands usually shrubby, with numerous slender stems.
2. [Ceanothus thyrsiflorus] Eschs. Blue Myrtle. California Lilac.
Leaves oblong or oblong-ovate, minutely glandular-serrate, smooth and lustrous on the upper surface and paler and slightly pubescent on the lower surface, especially along the 3 prominent ribs, 1′—1½′ long and ½′—1′ wide; petioles stout, ⅓′—½′ in length; stipules membranaceous, acute. Flowers blue or white, appearing in early spring in small pedunculate corymbs from the axils of minute deciduous bracts, and collected into slender rather loose thyrsoid clusters 2′—3′ long in the axils of upper leaves or of small scarious bracts, and usually surmounted by the terminal leafy shoot of the branch. Fruit ripening from July to December, black; seeds 1/12′ long, smooth, dark brown or nearly black.
A tree, occasionally 35° high, with a trunk 12′—14′ in diameter, dividing 5°—6° from the ground into many small wide-spreading branches, and conspicuously angled pale yellow-green branchlets slightly pubescent when they first appear, soon becoming glabrous; more often a tall or low shrub. Bark of the trunk thin, with a bright red-brown surface separating into thin narrow appressed scales. Wood close-grained, rather soft, light brown, with thin darker colored sapwood.