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RHAMNACEAE BUCKTHORN FAMILY

John O. Sawyer, Jr., except as noted

[Perennial herb] shrub, tree, generally erect, often thorny. Leaf: simple, generally alternate, often clustered on short-shoots; stipules generally present, occasionally modified into spines; generally petioled; blade pinnate-veined or 1–5-ribbed from base. Inflorescence: cyme, panicle, umbel, or flowers 1 or clustered in axils or on short-shoots. Flower: generally bisexual, radial; hypanthium subtending, surrounding, or partly fused to ovary; sepals 4–5; petals 0, 4–5, generally clawed; stamens 0, 4–5, alternate sepals, attached to hypanthium top, each generally fitting into a petal concavity; disk (0 or) between stamens, ovary, thin to fleshy, entire or lobed, free from ovary, adherent or fused to hypanthium; ovary superior or ± inferior, chambers [1]2–4, 1–2-ovuled, style 1, stigma entire or 2–3-lobed. Fruit: capsule, drupe.
50–52 genera, 950 species: especially tropics, subtropics some cultivated (Ceanothus; Frangula; Rhamnus; Ziziphus). [Richardson et al. 2000 Amer J Bot 87:1309–1324] —Scientific Editors: Steve Boyd, Thomas J. Rosatti.
Unabridged references: [Brizicky 1965 J Arnold Arbor 45:439–463; Richardson et al. 2000 Kew Bull 55:311–341]

Key to Rhamnaceae

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

R. alnifolia L'Hér. ALDER BUCKTHORN
NATIVE
Shrub, < 2 m. Stem: bark gray; branches puberulent to glabrous; twigs brown; winter bud scales ± 5 mm. Leaf: deciduous; petiole 4–15 mm; blade 45–110 mm, elliptic to ovate, thin enough to transmit light, glabrous to puberulent, base acute to obtuse, tip acute, margin irregularly toothed, veins prominent, arched. Inflorescence: 1–3-flowered; pedicels 2–10 mm. Flower: unisexual; hypanthium ± 1 mm wide; sepals 5; petals 0, 4, 5. Fruit: 3-stoned, ± 8 mm, black.
Wet meadow edges, seeps, stream sides; 1450–2020 m. n High Sierra Nevada; to Canada, northern Rocky Mountains, northern United States. May–Jul [Online Interchange] {CNPS list}
Unabridged synonyms: [Apetlorhamnus alnifolia (L'Hér.) Nieuwl.]

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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html, accessed on Oct 30 2014
Citation for this treatment: [Author of taxon treatment] 2013. Rhamnus, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?tid=41067, accessed on Oct 30 2014

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click for enlargement Rhamnus alnifolia
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2000 Dean Wm. Taylor

Geographic subdivisions indicated for the distribution of Rhamnus alnifolia Markers link to CCH specimen records. If the markers are obscured, reload the page [or change window size and reload]. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.
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map of distribution 1
(Note: any qualifiers in the taxon distribution description, such as 'northern', 'southern', 'adjacent' etc., are not reflected in the map above, and in some cases indication of a taxon in a subdivision is based on a single collection or author-verified occurence).

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Data provided by the participants of the Consortium of California Herbaria.
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CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.