Jepson eFlora: Taxon page
Vascular Plants of California
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Rhamnus pilosa

Higher Taxonomy
Family: RhamnaceaeView DescriptionDichotomous Key
Habit: [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.
Genera In Family: 50--52 genera, 950 species: especially tropics, subtropics some cultivated (Ceanothus; Frangula; Rhamnus; Ziziphus).
eFlora Treatment Author: John O. Sawyer, Jr., except as noted
Scientific Editor: Steve Boyd, Thomas J. Rosatti.
Genus: RhamnusView DescriptionDichotomous Key

Common Name: BUCKTHORN
Habit: 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 pls, 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.
Etymology: (Greek: name for plants of this genus) Note: 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.
eFlora Treatment Author: John O. Sawyer, Jr.
Reference: Bolmgren & Oxelman 2004 Taxon 53:383--390
Unabridged Reference: Wolf 1938 Rancho Santa Ana Bot Gard Monogr 1
Rhamnus pilosa (Trel. ex Curran) Abrams
Habit: Shrub, < 2 m. Stem: bark gray; branches few, generally flexible, generally ascending; twigs densely hairy. Leaf: evergreen; petiole 2--5 mm, hairy; blade 15--20 mm, ovate to round, thick, soft-hairy, abaxially flat to concave, base, tip rounded to acute, margin finely toothed, flat to rolled under, veins not prominent. Inflorescence: 1--6-flowered, soft-hairy; pedicel 2--4 mm. Flower: generally unisexual; hypanthium +- 2 mm wide; sepals 4; petals 0, 4. Fruit: 2-stoned, 6 mm, red.
Ecology: Uncommon. Chaparral; Elevation: 75--1650 m. Bioregional Distribution: s PR (San Diego Co.). Flowering Time: Jan--Mar
Synonyms: Rhamnus crocea Nutt. subsp. pilosa (Trel. ex Curran) C.B. Wolf; Rhamnus crocea var. pilosa Trel. ex Curran
Unabridged Note: Sp. not known from Baja California or Arizona as reported in USDA Plants Database based on note in Abrams, L. 1960. An illustrated flora of the Pacific States. No specimens support the claim, but some specimens from RSA-POM approach Rhamnus pilosa morphologically.
Jepson eFlora Author: John O. Sawyer, Jr.
Reference: Bolmgren & Oxelman 2004 Taxon 53:383--390
Index of California Plant Names (ICPN; linked via the Jepson Online Interchange)

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Botanical illustration including Rhamnus pilosa

botanical illustration including Rhamnus pilosa

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Citation for this treatment: John O. Sawyer, Jr. 2012, Rhamnus pilosa, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on February 23, 2024.

Citation for the whole project: Jepson Flora Project (eds.) 2024, Jepson eFlora,, accessed on February 23, 2024.

Rhamnus pilosa
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©2016 Keir Morse
Rhamnus pilosa
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©2016 Keir Morse
Rhamnus pilosa
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©2016 Keir Morse
Rhamnus pilosa
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©2016 Keir Morse
Rhamnus pilosa
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©2013 Keir Morse

More photos of Rhamnus pilosa
in CalPhotos

Geographic subdivisions for Rhamnus pilosa:
s PR (San Diego Co.).
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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).


Data provided by the participants of the  Consortium of California Herbaria.
View all CCH records
All markers link to CCH specimen records. The original determination is shown in the popup window.
Blue markers indicate specimens that map to one of the expected Jepson geographic subdivisions (see left map). Purple markers indicate specimens collected from a garden, greenhouse, or other non-wild location.
Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.

CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa, if there are more than 1 infraspecific taxon in CA.
Blue line denotes eFlora flowering time (fruiting time in some monocot genera).