|Alder Buckthorn (Rhamnus frangula)|
Rhamnus is a genus of about 150 species (less, if some species are placed in Frangula), which are shrubs or small trees, commonly known as buckthorns. It is part of the family Rhamnaceae. Its species range from 1–10 m tall (rarely to 15 m) and are native mainly in east Asia and North America, but found throughout the temperate and subtropical Northern Hemisphere, and also more locally in the subtropical Southern Hemisphere in parts of Africa and South America.
Both deciduous and evergreen species occur. The leaves are simple, 3–15 cm long, and arranged either alternately or in opposite pairs. One distinctive character of many buckthorns is the way the veination curves upward towards the tip of the leaf. The plant bears fruits which are dark blue berries. The name is due to the woody spine on the end of each twig in many species.
Rhamnus species are shrubs or small to medium-sized trees, with deciduous or rarely evergreen foliage. Branches are unarmed or end in a woody spine. Leaves opposite or alternately arraigned, a few species have clusters of leaves arising from the same point on short shoots. The leaf blades are undivided and pinnately veined. Leaf margins are serrate or rarely entire. Most species have yellowish green, small, bisexual or unisexual, rarely polygamous flowers; which are produced singly or in axillary cymes, cymose racemes, or cymose panicles containing a few flowers. Calyx tube campanulate to cup-shaped, with 4 or 5 ovate-triangular sepals, which are adaxially ± distinctly keeled. Petals 4 or 5 but a few species may lack petals. The petals are shorter than the sepals. Flowers have 4 or 5 stamens which are surrounded by and equal in length the petals or are shorter. The anthers are dorsifixed. The superior ovary is free, rounded, with 2-4 chambers. Fruits are a 2-4 stoned, berrylike drupe, which is obovoid-globose or globose shaped. Seeds are obovoid or oblong-obovoid shaped, unfurrowed or abaxially or laterally margined with a long, narrow, furrow. The seeds have fleshy endosperm.
Rhamnus has a nearly cosmopolitan distribution, with about 150 species which are native from temperate to tropical regions, the majority of species are from east Asia and North America, with a few species in Europe and Africa.
North American species include Alder-leaf Buckthorn (R. alnifolia) right across the continent, Carolina Buckthorn (R. (F.) caroliniana) in the east, Cascara Buckthorn (R. (F.) purshiana) in the west, and the evergreen California Buckthorn or Coffeeberry (R. (F.) californica) and Hollyleaf Buckthorn (R. crocea) in the west.
In South America, Rhamnus diffusus is a small shrub native from the Valdivian temperate rain forests in Chile.
Buckthorns may be confused with Dogwoods, which share the curved leaf venation; indeed, "dogwood" is a local name for R. prinoides in southern Africa, a plant used to make Ethiopian mead and known as "gesho" in Ethiopia. The two plants are easy to distinguish by slowly pulling a leaf apart; in dogwood thin white latex strings can be seen, strings not present in buckthorn.
|This section does not cite any references or sources. (November 2012)|
The genus is divided into two subgenera, sometimes treated as separate genera:
- Subgenus Rhamnus: flowers with four petals, buds with bud scales, leaves opposite or alternate, branches with spines. Species include:
- Rhamnus alaternus – Italian Buckthorn
- Rhamnus alnifolia – Alderleaf Buckthorn
- Rhamnus arguta – Sharp-tooth Buckthorn
- Rhamnus cathartica – Common (or Purging) Buckthorn (syn. R. catharticus)
- Rhamnus crocea – Redberry Buckthorn (ssp. crocea), Hollyleaf Buckthorn (ssp. pilosa)
- Rhamnus davurica – Dahurian Buckthorn
- Rhamnus diffusus
- Rhamnus globosa – Lokao Buckthorn
- Rhamnus ilicifolia – Hollyleaf Redberry
- Rhamnus japonica – Japanese Buckthorn
- Rhamnus lanceolata – Lanceleaf Buckthorn
- Rhamnus libanotica
- Rhamnus lycioides
- Rhamnus palaestinus - endemic to Israel
- Rhamnus petiolaris - endemic to Sri Lanka
- Rhamnus pirifolia – Island Redberry Buckthorn
- Rhamnus prinoides – Shiny-leaf Buckthorn
- Rhamnus saxatilis – Rock Buckthorn, Avignon Buckthorn, Avignon Berry (syn. R. infectoria, R. infectorius)
- Rhamnus serrata – Sawleaf Buckthorn
- Rhamnus smithii – Smith's Buckthorn
- Rhamnus staddo – Staddo (syn. R. rhodesicus)
- Rhamnus utilis – Chinese Buckthorn
- Subgenus Frangula: flowers with five petals, buds without bud scales, leaves always alternate, branches without spines. Species include:
- Rhamnus betulaefolia (Frangula betulifolia) – Birchleaf Buckthorn
- Rhamnus californica (Frangula californica) – California Buckthorn, Coffeeberry
- Rhamnus caroliniana (Frangula caroliniana) – Carolina Buckthorn, Indian Cherry (syn. R. carolinianus)
- Rhamnus frangula (Frangula alnus) – Alder Buckthorn, Glossy or Breaking Buckthorn, Black Dogwood
- Rhamnus glandulosa - Sanguinho
- Rhamnus purshiana (Frangula purshiana) – Cascara Buckthorn (syn. R. purshianus)
- Rhamnus rubra (Frangula rubra) – Red Buckthorn
Some species are invasive outside their natural ranges.
The fruit of most species contain a yellow dye and the seeds are rich in protein. Oils from the seeds are used for making lubricating oil, printing ink, and soap.
Some species may cause demyelinating polyneuropathies. The Purging Buckthorn or Common Buckthorn (R. cathartica) is a widespread European native species, in the past used as a purgative, though its toxicity makes this a very risky herbal medicine and it is no longer used. Introduced into the United States as a garden shrub, this has become an invasive species in many areas there. It has recently been discovered to be a primary host of the soybean aphid (Aphis glycines), a problem pest for soybean farmers across the US. The aphids use the buckthorn as a host for the winter and then spread to nearby soybean fields in the spring.
Another European species, Alder Buckthorn (R. frangula, syn. Frangula alnus) was of major military importance in the 15th to 19th centuries, as its wood provided the best quality charcoal for gunpowder manufacture.
Dyer's Buckthorn (R. tinctoria) is used, together with the Asian Chinese Buckthorn (R. utilis), to produce the dye "china green". Another species, Avignon Buckthorn (R. saxatilis) provides the yellow dye Persian berry, made from the berries.
- "Rhamnus in Flora of China @". Efloras.org. Retrieved 2013-05-07.
- "Rhamnus in Flora of Pakistan @". Efloras.org. Retrieved 2013-05-07.
- "Peripheral Neuropathy: Peripheral Nervous System and Motor Unit Disorders: Merck Manual Professional". Merckmanuals.com. Retrieved 2013-05-07.
- Box: 2207A (2012-04-03). "SDSU Department of Plant Science: Managing Soybean Aphids". Sdstate.edu. Retrieved 2013-05-07.
- Francis Montagu Smith (1871). A handbook of the manufacture and proof of gunpowder, as carried on at the Royal Gunpowder Factory, Waltham Abbey. H.M. Stationery Office. pp. 26–. Retrieved 2 April 2013.
- Synergy International Limited <http://www.synergy.co.nz> (2006-03-23). "issg Database: Ecology of Rhamnus alaternus". Issg.org. Retrieved 2013-05-07.
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|Wikisource has the text of the 1911 Encyclopædia Britannica article Buckthorn.|