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. alnifolia L'Hér.

ALDER BUCKTHORN

Shrub < 2 m
Stem: bark gray; twigs brown; terminal bud scales 5 mm
Leaves deciduous; petiole 4–12 mm; blade 45–100 mm, ovate to elliptic, thin enough to transmit light, base acute to obtuse, tip acute, margin irregularly toothed, sides glabrous to puberulent, veins prominent, arched
Inflorescence 1–3-flowered; pedicels 2–10 mm
Flower unisexual; hypanthium 1 mm; sepals 5; petals 0; style exserted
Fruit 3-stoned, ± 8 mm, black
Ecology: Uncommon. Wet meadow edges of lodgepole-pine forest
Elevation: 1800 m.
Bioregional distribution: n High Sierra Nevada (Nevada, Placer cos.)
Distribution outside California: to Canada, n Rocky Mtns, n US
Horticultural information: WET, DRN: 1, 2, 7, 15, 16 &SUN: 4, 6.