Article from Bean's Trees and Shrubs Hardy in the British Isles
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'Ceanothus megacarpus' from the website Trees and Shrubs Online (treesandshrubsonline.
An evergreen shrub up to 12 ft high; branches slender, finely downy when young. Leaves alternate, entire, obovate to oval, tapered at the base, rounded or notched at the apex, 1⁄2 to 11⁄4 in. long, glabrous above; the under-surface is finely and closely downy and prettily marked with numerous, closely set, parallel veins; stalk 1⁄8 in. or less long. Flowers white, 1⁄5 in. wide, produced in several umbels each about 1⁄2 in. wide on short twigs from late March to May; stalks glabrous, very slender. Fruit up to 3⁄8 in. wide, subglobose with a distinct rim and several horns.
Native of California, originally collected by Wm Lobb in the early fifties of last century. It needs wall protection, preferably south, in most parts of Britain and is about the earliest to flower in this country.