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Rhamnaceae from the genus Rhamnus,the old Greek name). Buckthorn Family. Fig. 36. Trees or shrubs, rarely herbs, sometimes spiny or climbing: leaves simple, mostly alternate: flowers bisexual or unisexual, regular, perigynous, small, greenish, mostly axillary; sepals 5, rarely 4, valvate; petals 5, or 4, alternate with the sepals; stamens of the same number as the petals and opposite them; an intrastaminal disk lining the cup-shaped receptacle; ovary 2-4-celled, superior or inferior; cells 1-, rarely 2-, ovuled; styles 2-4, more or less connate: fruit drupaceous, or winged, or capsular.
Rhamnaceae has 46 genera and about 550 species very generally distributed over the earth. Rhamnus is the largest genus (70 species), and the most widely distributed. The family is represented by 6 native species in northeastern North America. It is most closely related to the Vitaceae and Celastraceae, differing from the former in the simple entire leaves and strongly perigynous flowers, and from the latter in the stamens being opposite the petals.
The family is not of great economic importance. The berries and bark of Rhamnus cathartica (buckthorn) contain a bitter principle which is purgative. The fruits of some species of Rhamnus yield yellow or green dyes of some importance R. dahurica and R. tinctoria give Chinese green. The bark of R. cathartica and R. Frangula (Europe) is used to dye yellow. R. Purshiana (California) is the cascara segrada of medicine, a strong purgative. The fruits of Zizyphus Lotus are pulpy and agreeable, and were much prized by the ancients. The fruits of several species of Zizyphus are eaten in various parts of the Old World. The spiny branches of Paliurus Spina-Christi or Zizyphus Spina-Chrisli are thought to have been those from which the crown of thorns was made.
Nine or more genera are in cultivation in N. America for ornamental purposes. These are: Ceanothus (New Jersey Tea); Berchemia (Supple Jack); Gouania; Hovenia; Paliurus; Pomaderris; Reynosia; Rhamnus (Buckthorn); Zizyphus (Jujube).
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