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Rhamnus (plant)

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File:Rhamnus pumila fruits.jpg
Rhamnus pumila, dwarf buckthorn

Rhamnus is a genus of about 140 accepted species of shrubs or small trees, commonly known as buckthorns, in the family Rhamnaceae. Its species range from Template:Cvt tall (rarely to Template:Cvt) 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. One species, the common buckthorn (Rhamnus cathartica), is able to flourish as an invasive plant in parts of Canada and the United States, where it has become naturalized.<ref name=":0" />

Both deciduous and evergreen species occur. The leaves are simple, Template:Cvt long, and arranged alternately, in opposite pairs, or almost paired (subopposite). 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 black or red berry-like drupes. The name is due to the woody spine on the end of each twig in many species. One species is known to have potential to be used medicinally.<ref name=":12" />

DescriptionEdit

Rhamnus species are shrubs or small to medium-sized trees,<ref>Template:Cite journal</ref> with deciduous or rarely evergreen foliage. Branches are unarmed or end in a woody spine. The leaf blades are undivided and pinnately veined. Leaf margins are serrate or rarely entire. Rhamnus species are generally dioecious, with male and female flowers on separate plants.<ref>Template:Cite journal</ref> Most species have yellowish green, small, unisexual or 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.<ref name="efloras">Template:Efloras</ref>

SpeciesEdit

Template:As of, Plants of the World Online accepted the following species:<ref name="POWO_30006159-2">Template:Cite POWO</ref> Template:Div col

|CitationClass=web }}</ref> purging buckthorn (orth. var. R. catharticus)

Template:Div col end

DistributionEdit

Rhamnus has a nearly cosmopolitan distribution,<ref>Template:Efloras</ref> with about 140 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.<ref name="efloras" />

North American species include Rhamnus alnifolia, alder-leaf buckthorn, occurring across the continent, and Rhamnus crocea, hollyleaf buckthorn, in the west. Though not native to this region, Rhamnus cathartica can be found in North America.<ref name=":2">Template:Cite journal</ref>

Buckthorns may be confused with dogwoods, which share the curved leaf venation; indeed, "dogwood" is a local name for R. prinoides in southern Africa. The two plants are easy to distinguish by slowly pulling a leaf apart; dogwoods will exude thin, white latex strings, while buckthorns will not.

Invasive speciesEdit

Rhamnus cathartica, the common buckthorn, is considered an invasive species in the United States<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and by many local jurisdictions and state governments, including Minnesota<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and Wisconsin.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The common buckthorn is well-adapted to spreading in Canada and the U.S.<ref name=":0">Template:Cite journal</ref> It is an efficient grower that does not need much sunlight and or fertile soil.<ref name=":0" /> Its seeds are hardy, as well as being able to grow and spread easily in a variety of environmental conditions.<ref name=":0" /> Also other animals prefer to leave buckthorns alone because their leaves are not appetizing and their fruits are toxic to some animals.<ref name=":0" /> Overall they are known to have a negative effect on their surrounding environment.<ref name=":0" /> For example, the European buckthorn is blamed for increased frog egg mortality from a chemical it releases.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Other species, such as the Rhamnus alaternus also make chemicals that prevent other animals from consuming them.<ref name=":12">Template:Cite journal</ref>

EcologyEdit

Some species are invasive outside their natural ranges. R. cathartica was introduced into the United States as a garden shrub and has become an invasive species in many areas there. It is a primary host of the soybean aphid (Aphis glycines), a 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Italian buckthorn (R. alaternus), an evergreen species from the Mediterranean region, has become a serious weed in some parts of New Zealand,<ref>Template:GISD</ref> especially on Hauraki Gulf islands.

Buckthorns are used as food plants by the larvae of many Lepidoptera species.

The American species are known to be hosts for the oat fungus Puccinia coronata. In a 1930 study, both kerosene and salt were employed for eradication of R. lanceolata and both proved to be less expensive than felling these bushes.<ref>Template:Cite book</ref>

UsesEdit

File:Rhamnus catharticus leaves and fruit.jpg
Rhamnus cathartica

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.<ref name="efloras" /> Many species have been used to make dyes. R. utilis provides china green, a dye used to give a bright green color to silk and wool.<ref name=bru>Template:Cite book</ref> The bark of some species of Rhamnus afford a beautiful yellow dye.<ref>Encyclopædia Britannica (1823), p. 139 (s.v. Rhamnus) (Template:JSTOR)</ref> Another species, Avignon buckthorn (R. saxatilis) produces a yellow dye, made from the fruit Persian berry.

Some species may cause demyelinating polyneuropathies.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The purging buckthorn (R. cathartica) is a widespread European native species used in the past as a purgative. It was in mid 17th-century England the only native purgative.<ref>Phil. trans. : Number 23, beginning the third year, March 11, 1666 at p.409, p.424</ref> It was also known pre-Linnaeus as Spina Cervina.<ref>Elizabeth Blackwell, "A Curious Herbal, Containing Five Hundred Cuts Of The Most Useful Plants" Template:Webarchive, p.134</ref> The berries of Spina Cervina are black and contain a greenish juice, along with four seeds apiece; this serves to distinguish them from those of the black alder and dogberry, which contain only one or two apiece. Its syrup is said to be churlish.<ref>William Lewis, "An Experimental History Of The Materia Medica"</ref> Its toxicity makes this a very risky herbal medicine, and it is no longer in use.<ref name=pfaf>Plants for a Future: Rhamnus cathartica</ref>

Rhamnus prinoides is known as gesho in Ethiopia, where it is used to make a mead called tej.

The species Rhamnus alaternus shows some promise for medicinal use as well.<ref name=":12" />

See alsoEdit

  • Sea buckthorn or Hippophae, an unrelated genus of shrubs with a similar common name
  • Frangula, a genus formerly included in Rhamnus

ReferencesEdit

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External linksEdit

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