The tribe Trichocereeae contains some of the most interesting columnar cacti of South America, and Espostoa certainly is among the most beautiful. I have marveled at the white stems and lateral cephalia of these cacti, growing in harsh, dry deserts. The group has not been well studied, and researchers have described several different genera to contain what are now believed to be members of Espostoa. Nathaniel Britton and Joseph Rose described Espostoa (type, Cactus lanatus — E. lanata) with a single species in 1920, naming it in honor of the Peruvian botanist, Nicolas E. Esposto. The International Cactaceae Systematics Group accepts 16 species, one (E. baumannii) of questionable status and perhaps a naturally occurring intergeneric hybrid. The cacti are shrubby or treelike, columnar, many-ribbed, and very spiny. They produce distinctive lateral cephalia that bear tubular to bell-shaped flowers, usually open at night in summer. The fruits may be naked or have tufts of hair.

Espostoa Britton & Rose 1920 Pseudoespostoa Backeberg 1934 Thrixanthocereus Backeberg 1937 Vatricania Backeberg 1950

Subfamily Cactoideae, tribe Trichocereeae. Plants treelike or shrubby, usually freely branching from the base or higher, to 4 m (13 ft) high. Stems erect, cylindrical or columnar, many-ribbed, spiny. Ribs low. Areoles bearing numerous spines and long hairs that form a webbing overthe stem. Spines numerous, some stout, others hairlike. Fertile zones lateral cephalia, formed over several ribs that are reduced and modified. Flowers borne from the cephalia, usually open at night, tubularto bell shaped, reddish to white, sometimes small; floral tubes short; pericarpels and floral tubes with small acute scales and hairs, spines absent; perianth parts short, spreadingor recurved. Fruits globose to ovoid, juicy, green to red, more or less naked or with tufts of hair; perianth parts persistent. Seeds diverse, oval to almost hat shaped, dull brown. Distribution: south of the equator in southern Ecuador, Peru, and Bolivia.

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