The International Cactaceae Systematics Group has struggled over the problem of whether Pygmaeocereus should be accepted as distinct or placed in Haageocereus. At least until further research is done, it has been decided to keep the genus separate (Hunt 1999a). Pygmaeocereus (type, P. byle-sianus) was described by Harry Johnson and Curt Backeberg in 1957, the name having first been used by Johnson in his 1955 catalog, in which he listed a "Pygmaeocereus akersii" (= P. bylesianus7). The name is derived from the Latin pyg-maeus, dwarf, thus dwarf cereus.

I have seen Pygmaeocereus at several sites in coastal Peru; they often occur in fairly extensive populations, though difficult to find. The region in which P. bylesianus occurs gets little if any rainfall, with vegetation dependent on the frequent, though seasonal, fogs. Three species are recognized, the genus characterized as having small, often clustering, globose to short cylindrical stems that bear night-blooming flowers with long, slender floral tubes.

Pygmaeocereus H. Johnson & Backeberg 1957

Subfamily Cactoideae, tribe Trichocereeae. Plants small, solitary to clustering, often barely rising above ground level, usually with fleshy roots. Stems globose, green, 1-5 cm (0.4-2 in) in diameter. Ribs 8-15, often forming tubercles. Areoles round to elongate, woolly. Spines several, usually differentiated as centrals and radials, often radiating, to 5 mm long. Flowers open at night, broadly funnelform, white, to 8 cm (3.1 in) longand 6 cm (2.4 in) in diameter; floral tubes long, slender. Fruits globose to pearshaped. Distribution: Peru.

Continue reading here: Pygmaeocereus bieblii Diers 1995

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