Rhamnaceae
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The Rhamnaceae are a large family of flowering plants, mostly trees, shrubs, and some vines, commonly called the buckthorn family.<ref name=FPSMM/> Rhamnaceae is included in the order Rosales.<ref>Template:Cite journal</ref>
The family contains about 55 genera and 950 species.<ref name="Christenhusz-Byng2016">Template:Cite journal</ref> The Rhamnaceae have a worldwide distribution, but are more common in the subtropical and tropical regions. The earliest fossil evidence of Rhamnaceae is from the Late Cretaceous. Fossil flowers have been collected from the Upper Cretaceous of Mexico and the Paleocene of Argentina.<ref>Template:Cite journal</ref>
Leaves of family Rhamnaceae members are simple, i.e., the leaf blades are not divided into smaller leaflets.<ref name=FPSMM>Flowering Plants of the Santa Monica Mountains, Nancy Dale, 2nd Ed. 2000, p. 166</ref> Leaves can be either alternate or opposite. Stipules are present and modified into spines in many genera. In some (e.g. Paliurus spina-christi and Colletia paradoxa) spectacularly so. Colletia stands out by having two axillary buds instead of one, one developing into a thorn, the other one into a shoot.
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The flowers are radially symmetrical. There are 5 (sometimes 4) separate sepals and 5 (sometimes 4 or none) separate petals. The petals may be white, yellowish, greenish, pink or blue, and are small and inconspicuous in most genera, though in some (e.g. Ceanothus) the dense clusters of flowers are conspicuous. The 5 or 4 stamens are opposite the petals.<ref name=FPSMM/> The ovary is mostly superior, with 2 or 3 ovules (or one by abortion).
The fruits are mostly berries, fleshy drupes, or nuts. Some are adapted to wind carriage, but most are dispersed by mammals and birds. Chinese jujube is the fruit of the jujube tree (Ziziphus jujuba) and is a major fruit in China.
The American genus Ceanothus, which has several showy ornamental species, has nitrogen-fixing root nodules.<ref>Template:Cite journal</ref>
Economic uses of the Rhamnaceae are chiefly as ornamental plants and as the source of many brilliant green and yellow dyes. The wood of Rhamnus was also the most favoured species to make charcoal for use in gunpowder before the development of modern propellants.
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Alphitonia ponderosa
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Ceanothus
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Ceanothus papillosus var. roweanus at the Regional Parks Botanic Garden, Berkeley, California
GeneraEdit
SystematicsEdit
Modern molecular phylogenetics recommend the following clade-based classification of Rhamnaceae:<ref>Template:Cite journal</ref>
Fossil recordEdit
The fossil record of the family extends back to the Late Cretaceous, with records from Colombia<ref>Template:Cite journal</ref> and Mexico.<ref>Template:Cite journal</ref> Remains from the mid-Cretaceous Burmese amber of Myanmar have been suggested to belong to this family by some authors<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>, but this has been doubted by others.<ref name=":0">Template:Cite journal</ref> The earliest fossils of modern genera of the family date to the Eocene.<ref>Template:Cite journal</ref>
ReferencesEdit
External linksEdit
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