The genus Myrtillocactus, subfamily Cactoideae (Console 1897), is represented by four species forming a homogeneous group: M cochal (Orcutt) Britton et Rose, M geometrizans (Martius) Console, M. schenckii (Purpus) Britton et Rose, and M. eichlamii Britton et Rose. The former three are distributed in Mexico, the latter in Guatemala. Brandegee (1900), considered M. cochal to be a variety of M. geometrizans, other authors (Buxbaum 1962, 1972, Hunt and Taylor 1986, 1990) see this as a monotypic genus integrated by M geometrizans. All are perennial, arborescent plants that grow in xerophilous scrub and spiny tropical forests (Rzedowski 1988). All four species in the genus are traditionally known as"garambullo." Their flowers and fruits are edible and their economic value is appreciated by rural people in the arid and semiarid zones of Mexico (Bravo-Hollis 1978, Bravo-Hollis and Sanchez-Mejorada 1991, Arias 1994). Myrtillocactus geometrizans has two varieties: M. geometrizans var. geometrizans (Martius) Console, and M. geometrizans var. grandiareolatus (Bravo) Backeberg, both including arborescent plants up to 4 m tall. Variety geometrizans occupies an ample range in the arid and semiarid zones of Mexico, distributed from the State of Tamaulipas to the State of Oaxaca. Katagiri (1952, 1953), reported for M. geometrizans chromosome numbers of 2n = 22 and 2n = 44 (autotetraploid). Ross (1981), in agreement with the basic number observed in other cacti (Pinkava et al. 1985, 1992), reports n = 11 and x = 11 for plants from a site in the State of Queretaro, Mexico. Diploid cytotypes have been observed in Echinocereus cinerascens, E. maritimus and E.
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