The nomenclature of the genus and species is somewhat tangled. In 1899,
Frédéric Weber described two species,
Cereus thouarsii and
Cereus galapagensis. His descriptions are brief and refer in part to information received from others; he also notes that neither the flowers nor the fruit of
Cereus galapagensis were known. The specific epithet
thouarsii refers to
Abel Aubert du Petit-Thouars, who found both species some 30 years earlier when his ship visited the Galápagos. In 1920,
Nathaniel Lord Britton and
Joseph Nelson Rose erected the genus
Brachycereus,
synonymizing both Weber's
Cereus thouarsii and another cactus from the Galápagos,
Cereus nesioticus, under the name
Brachycereus thouarsii. They placed Weber's
Cereus galapagensis in a separate new genus,
Jasminocereus, as
Jasminocereus galapagensis. In 1935,
Curt Backeberg realized that only
Cereus nesioticus was the
Brachycereus of Britton and Rose, and later placed Weber's
Cereus thouarsii in
Jasminocereus. In 1971, Anderson and Walkington carried out fieldwork and studied herbarium material, and decided that Weber's two species were actually the juvenile and mature forms of the same species. The earliest epithet for the species is
thouarsii. Additional species of
Jasminocereus have been described, but they are now regarded as part of a single species, which may be divided into three varieties.
J. sclerocarpus is then a synonym of
J. thouarsii var.
sclerocarpus and
J. howellii of
J. thouarsii var.
delicatus. Other sources do not recognize distinct varieties.
Phylogeny and classification Molecular studies show that the two endemic Galápagos genera,
Jasminocereus and
Brachycereus, are sisters, with their closest relative being the South American mainland species
Armatocereus: }} In one widely used classification of cacti,
Armatocereus and
Jasminocereus are placed in the tribe Browningieae of the subfamily
Cactoideae, and
Brachycereus is placed in the tribe Trichocereeae, which is inconsistent with the cladogram above. A classification produced in 2010 by Nyffeler and Eggli puts all three genera in a much larger tribe Phyllocacteae. ==Distribution and habitat==