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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]

RHAMNUS

BUCKTHORN

Shrub, small tree
Stem: branches alternate, flexible; twigs sometimes thorn-tipped
Leaves sometimes clustered on short-shoots, deciduous or evergreen, petioled; stipules deciduous; blade 1-ribbed from base, entire or not
Inflorescence: umbel or flowers solitary, axillary
Flower bisexual or unisexual, generally < 3 mm; hypanthium at base fused to, developing around ovary in fruit, above base deciduous; sepals 4 or 5; petals 0, 4, or 5; stamens 4 or 5; ovary appearing partly inferior, chambers 2–4, each 1–2-ovuled, style lobes 2–4
Fruit: drupe, 2–4-stoned
Species in genus: 125 species: temp, few tropical
Etymology: (Greek: name for plants of this genus)
Reference: [Wolf 1938 Rancho Santa Ana Bot Gard Monogr 1]
Some of value in medicine or as dyes.

Native

R. purshiana DC.

CASCARA

Tree or shrub, < 12 m
Stem: bark gray; twigs red to brown; terminal bud not covered with scales, hairs brown
Leaves deciduous; petiole 6–23 mm; blade 50–150 mm, broadly elliptic to obovate, thin, base obtuse or tapered, tip obtuse to truncate, margin irregularly toothed to entire, surfaces sparsely hairy to glabrous, veins prominent
Inflorescence < 25-flowered; pedicels < 25 mm
Flower bisexual; hypanthium 3 mm; sepals 5; petals 5; stamens 5; style included
Fruit 3-stoned, 10 mm, black
Ecology: Coniferous forests, chaparral
Elevation: < 2000 m.
Bioregional distribution: North Coast, Klamath Ranges, Outer North Coast Ranges, High North Coast Ranges, Cascade Range, n&c Sierra Nevada
Distribution outside California: to British Columbia, Montana
Plants with wedge-shaped leaves in KR, CaR, n&c SN assignable with difficulty to var. annonifolia (Greene) Jeps. Bark yields cathartic drugs; bark and fruit TOXIC in excess, especially to children
Horticultural information: 4, 5 &IRR: 1, 2, 3, 6, 16, 17 &SHD: 7, 14, 15.

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