Cephalanthus is a genus of flowering plants in the family Rubiaceae. There are five extant species that are commonly known as buttonbush.
Description They are shrubs or small trees growing to tall. The leaves are simple, arranged in opposite pairs or whorls of three. The flowers form a dense globular inflorescence.
Distribution and habitat Cephalanthus occidentalis is native to the eastern United States and Canada. The others occur in tropical regions of the Americas, Africa and Asia. Two species are known in cultivation.Huxley AJ et al. (eds.) The New Royal Horticultural Society Dictionary of Gardening. The Macmillan Press Limited, London; The Stockton Press, New York. 1992.
Systematics Cephalanthus was named by Linnaeus in Species Plantarum in 1753. The generic name is derived from the Ancient Greek words κέφαλη (kephale), meaning "head", and ἄνθος (anthos), meaning "flower".
Taxonomy Cephalanthus is the most basal genus in the tribe Naucleeae. Some authors have segregated it into its own monotypic tribe. The type species is Cephalanthus occidentalis.
Species The following five extant species are accepted:
Cephalanthus angustifolius Lour. – Laos, Cambodia, Vietnam Cephalanthus glabratus (Spreng.) K.Schum. – sarandí – Brazil, Argentina, Paraguay, Uruguay Cephalanthus occidentalis L. – button-willow, common buttonbush, honey-bells – Cuba, eastern Canada, eastern, central and southern United States, California, Arizona, New Mexico Cephalanthus salicifolius Humb. & Bonpl. – Mexican buttonbush, willowleaf buttonbush – Mexico, Honduras, extreme southern tip of Texas Cephalanthus tetrandrus (Roxb.) Ridsdale & Bakh.f. – tropical Asia from India to China and Thailand
Fossil record Sixteen fossil mericarps of †Cephalanthus pusillus have been described from middle Miocene strata of the Fasterholt area near Silkeborg in Central Jutland, Denmark.Friis, Else Marie, 1985, Angiosperm Fruits and Seeds from the Middle Miocene of Jutland (Denmark), The Royal Danish Academy of Sciences and Letters 24:3
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