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Key to families | Table of families and genera

Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.

 

RHAMNUS BUCKTHORN
Shrub, small tree, < 10 m. Stem: branches alternate, stiff or flexible; twigs generally not thorn-tipped; winter bud scales present, generally ± 3 mm. Leaf: scattered along branches or clustered on short-shoots, deciduous or evergreen; stipules generally deciduous; petioles generally glabrous; blade veins prominent or not. Inflorescence: flowers 1 or in cyme-like clusters in axils. Flower: unisexual (bisexual), generally on separate plants, generally < 3 mm; hypanthium bell-shaped to cup-like, 2–3 mm wide; sepals 4–5, thin, spreading, not keeled adaxially; petals 0 or 4–5; disk thin, adhering to hypanthium; ovary appearing superior or partly inferior, chambers 2–4, each 1-ovuled, style 1, stigma 2–4-lobed. Fruit: drupe, 2–3[4]-stoned.
110 species: temperate, few tropics; some of value in medicine or as dyes. (Greek: name for plants of this genus) [Bolmgren & Oxelman 2004 Taxon 53:383–390] W.H. Brewer collected Rhamnus cathartica L., considered invasive in parts of United States, in 1861, but it apparently never naturalized. Other taxa in TJM (1993) moved to Frangula.
Unabridged references: [Wolf 1938 Rancho Santa Ana Bot Gard Monogr 1]

Key to Rhamnus

1. Leaves deciduous; sepals 5; fruit black, 3-stoned ..... R. alnifolia

1' Leaves evergreen; sepals 4–5; fruit red, 2-stoned, or black, 3-stoned

2. Leaf blade 20–60 mm, elliptic or ovate to lance-ovate; sepals 5; fruit black, 3-stoned — Central Coast (Monterey Co.), South Coast (Newport Back Bay), expected elsewhere ..... [R. alaternus]

2' Leaf blade 10–40 mm, elliptic to round; sepals 4; fruit red, 2-stoned (Rhamnus crocea complex)

3. Leaf blade <= 15 mm, flat abaxially; branches spreading ..... R. crocea

3' Leaf blade >= 15 mm, flat to concave abaxially; branches generally ascending

4. Leaf blade elliptic; small tree; Channel Islands ..... R. pirifolia

4' Leaf blade elliptic to round; shrub; mainland

5. Leaf blade glabrous or hairy abaxially, glabrous adaxially; twigs glabrous to finely hairy; California Floristic Province, Desert Mountains ..... R. ilicifolia

5' Leaf blade soft hairy; twigs densely hairy; s Peninsular Ranges (San Diego Co.) ..... R. pilosa

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Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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