RHAMNACEAE

BUCKTHORN FAMILY

John O. Sawyer, Jr. (except Ceanothus)

Shrub, vine, tree, generally erect, often thorny
Leaves simple, generally alternate, often clustered on short-shoots, generally petioled, generally stipuled; blade often 1–3-ribbed from base
Inflorescence: cyme, panicle, or flowers solitary in axils
Flower generally bisexual, radial; hypanthium subtending, surrounding, or partly fused to ovary; sepals 4 or 5; petals 0, 4, or 5, clawed; stamens 4 or 5, alternate sepals, attached to hypanthium top, each generally fitting into a petal concavity; ovary superior or partly inferior, chambers 2–5, each 1–2-ovuled, style lobes or parts 1–3
Fruit: capsule, drupe
Genera in family: 55 genera, 900 species: especially tropical, subtropical; some cultivated (Ceanothus ; Colletia , anchor-plant; Gouania ; Phylica ; Rhamnus ; Ventilago ; Ziziphus )
Reference: [Brizicky 1965 J Arnold Arbor 45:439–463]

CEANOTHUS

CALIFORNIA-LILAC

Clifford L. Schmidt

Shrub, small tree, prostrate to erect, thorny or not
Stem: branches generally arranged as leaves
Leaves alternate or opposite, deciduous or evergreen, petioled; blade 1–3-ribbed from base, margin entire or not
Inflorescence: generally panicle-like aggregations of umbel-like, 3-flowered clusters
Flower generally < 5 mm; hypanthium surrounding fleshy disk below ovary base, in fruit thick, not splitting; sepals generally 5, lanceolate-deltate, incurved, colored like petals, persistent; petals generally 5, hooded, white to deep blue; stamens generally 5, opposite petals; ovary superior, 3-lobed, chambers 3, each 1-ovuled, style parts 3
Fruit: capsule, ± spheric, 3-valved
Seeds 3, ± 3 mm, 1 surface convex
Species in genus: 45 species: North America, especially w
Etymology: (Greek: thorny plant)
Reference: [Rensselaer & McMinn 1942 Ceanothus Santa Barbara Bot Gard 1–308]
Hybridization common (named hybrids not recognized here); hybrid forms may not key adequately.

Native

C. crassifolius Torr.

HOARYLEAF CEANOTHUS

Plant erect, open, < 3.5 m
Stem: twigs round, white- to rusty-tomentose, becoming gray to brown
Leaves opposite, evergreen, < 3 cm; stipules persistent; petiole 2–6 mm; blade ± ovate, 1-ribbed from base, firm, tip obtuse, margin turned under or not, generally with few shallow teeth, upper surface olive-green, glabrous, minutely rough, lower canescent to tomentose
Inflorescence raceme-like, < 3 cm
Flower white
Fruit 6–8 mm; horns on shoulder; ridges 0
Chromosomes: 2n=24
Ecology: Dry ridges, slopes
Elevation: < 1100 m.
Bioregional distribution: Outer South Coast Ranges (Santa Barbara Co.), Transverse Ranges, Peninsular Ranges
Distribution outside California: n Baja California
Less hairy plants with ± flat leaf margins in n of range have been called var. planus Abrams; plants < 1 m, with upper leaf surface tomentose in Otay Mtns, San Diego Co., may be hybrid, C. X otayensis McMinn
Horticultural information: DRN, DRY, SUN: 7, 8, 9, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24; STBL.