Rauhocereus

In 1957 Curt Backeberg described Rauhocereus, honoring Werner Rauh, professor of botany at the University of Heidelberg and a major contributor to our knowledge of succulent plants. The cactus has been brought into cultivation and it is handsomely columnar, producing large white flowers at night in summer.

Research has shown that Rauhocereus is closely related to Browningia; Gordon Rowley placed it in that genus in 1982. Arthur Gibson (1992), however, in his extensive analysis of the group of cacti related to Stenocereus, felt that Rauhocereus is a good genus. The International Cactaceae Systematics Group decided to recognize Rauhocereus because the single species has several features that distinguish it from Browningia.

Rauhocereus Backeberg 1957

Subfamily Cactoideae, tribe Trichocereeae.

Rauhocereus riosaniensis Backeberg 1957 Browningia riosaniensis (Backeberg) G. D. Rowley 1982 Rauhocereus riosaniensis vat. jaenensis Rauh ex Backeberg 1959, R. riosaniensis subsp.jaenensis (Rauh ex Backeberg) Ostolaza 1998

Plants mostly shrubby, usually branching basally, often forming thickets to 4 m (13 ft) high. Stems columnar, erect, bluish green, 8-15 cm (3.1-5.9 in) in diameter. Ribs 5-6, divided into many-faceted tubercles. Areoles with wool and a few stout spines. Spines 2-8, sometimes not readily distinguish-

Rauhocereus

able as centrals and radials, reddish below, yellowish above, all becoming grayish white, to 5 cm (2 in) long, variable in length and thickness. Flowers borne near the stem tips, open at night, bell shaped, 8-10 cm (3.1-3.9 in) long, to 5 cm (2 in) in diameter; pericarpels and floral tubes with small scales and curly brown hairs. Fruits ovoid, red, fleshy; floral remains persistent. Seeds small, ovoid, glossy black, shallowly tuberculate with tiny pits. Distribution: northern Peru.

Two subspecies of Rauhocereus riosaniensis are recognized. Subspecies riosaniensis has mostly 6 spines not easily distinguishable as centrals and radials; it occurs in the valley of the Rio Saña. Subspecies jaenensis has 2 very stout central spines and 2-3 radials; it occurs between Chamaya and Jaén.

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