Among the most popular cacti for hobbyists—and certainly exciting to see in the field—is Gymnocalycium, a large genus of globose cacti from east of the Andes in South America. Gymnocalycium (type, Echinocactus denudatus — G. denuda-tum) was described by Ludwig Pfeiffer in 1844 for three species, the name derived from the Greek gymnos, naked, and calyx, bud, referring to the smooth flower bud.

The great popularity of the cacti has led to a large number of names and several publications. Gerhart Frank (1976— 1977), Bohumil Schütz (1986), and John Pilbeam (1995) have published important treatments of Gymnocalycium, but one of the most valuable in assessing the status of the many names of species is the work by Detlev Metzing, Massimo Meregalli, and Roberto Kiesling (1995). There has been little debate as to the placement of Gymnocalycium in the tribe Trichocereeae, but determining which of the many species are acceptable is another matter. Metzing et al, and others, have greatly assisted the International Cactaceae Sys-tematics Group in developing its list of 71 accepted species.

348 Gymnocalycium

Gymnoccdycium is characterized as having low-growing, usually solitary stems with several ribs that are sometimes tuberculate. It has no differentiated fertile zone, the flowers simply arising from the usually depressed stem tip. Flowers are open during the day, funnelform to bell shaped, and white or pale pink. The pericarpels and floral tubes have a few broad, obtuse scales with membranous margins; their areoles are naked. Fruits are oblong to globose, either dry or fleshy, and dehiscent.

Gymnocalycium Pfeiffer ex Mittler 1844, as "Gymnocalicium" Brachycalycium Backeberg 1942

Subfamily Cactoideae, tribe Trichocereeae. Plants low growing, usually solitary but sometimes forming clusters. Stemsglobose to depressed globose to short cylindrical. Ribs 4-15, sometimes more, usually broadly rounded, often splraling, at times tuberculate, often with "chlns"just below the areoles. Tubercles often present, variable. Areoles large. Spines present, variable. Differentiated fertile zone absent. Flowers borne at or near the stem tips, open during the day in spring and summer, funnelform to bell shaped, white or pink, sometimes yellow or vivid red; pericarpels and floral tubes with a few large, broad, obtuse scales with membranous margins, areoles naked; perianth usually spreading; stamens in two groups, one surroundingthe nectar chamber, the other inserted nearthe mouth of the floral tube. Fruits oblong to globose, dry or fleshy, dehiscing by various means; floral remains persistent. Seeds extremely variable. Distribution: Bolivia, southern Brazil, Paraguay, Uruguay, and Argentina.

A number of infrageneric taxa of Gymnocalycium have been described, based mainly on seed characters, and these are described by Schütz (1986) and Pilbeam (1995). Six subgenera are often recognized: Gymnocalycium, Macrosemineum, Microsemineum, Musco-semineum, Pirisemineum, and Trichomosemineum.

Continue reading here: Gymnocalycium ambatoense Piltz 1980

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