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Wisconsin Plant of the Week

Rhamnus cathartica L.

Rhamnaceae (Buckthorn Family)

Common Name:

common buckthorn


Common buckthorn is a non-native shrub or small tree that grows to 6 m.  It's native to Eurasia and is cultivated in N. America as an ornamental where it's become an obnoxious weed -- the shrub equivalent of purple loosestrife.

Buckthorn  grows in thickets in woods, swamps and along rivers where, once established, it replaces the native woody understory.  Native ground cover species can't survive under buckthorn's dense shade. It's canopy is thick and along with Eurasian honeysuckles, it's among the first plants to leaf out in spring and the last to lose leaves in the fall.

Branches and leaves are opposite to sub-opposite, i.e. nearly opposite, but slightly staggered (see winter twig inset), a feature that's useful for winter identification and not found in any similar species. Short branches end in a sharp spine. In wetter soils closely spaced multiple trunks are common.

Leaves are simple, 3 to 6 cm long and broadly oval or round with closely spaced blunt teeth on the edges.  Most leaves have 3 pairs of lateral veins, each of which curves upward toward the leaf tip, similar to the veins in dogwoods.

Small greenish white 4-parted flowers bloom in May to June.  Common buckthorn is dioecious with male and female flowers on separate plants.

The fruit on the female plants are 5 to 6 mm drupes with 4 pits, each with one seed.  The fruit is first red and turns black when ripe.  Mature plants produce thousands of fruit, which are eaten and then distributed by birds. Passage through a birdís digestive system greatly increases the rate of germination.  Buckthorn also reproduces by sprouting from stumps and roots.

  • Origin of the name: Rhamnus, ancient Latin name for prickly shrubs; cathartica, Gr. katharsis, purification, refers to the laxative property of the bark and fruit.
  • Range:  Eurasia and wherever cultivated and escaped
  • WI Range:  Statewide, less common in the north
  • Common associates: Box elder, honeysuckle, arrow leaved aster
  • Wetland Indicator Status: FACU (FAC- on revised draft list)
  • Coefficient of Conservatism: C = * (S&W), C = * (MI)
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