An important figure of mushroom usage in Mexico was María Sabina, who used native mushrooms, such as "Psilocybe mexicana" in her practice. Present in varying concentrations in about 200 species of "Basidiomycota" mushrooms, psilocybin evolved from its ancestor, muscarine, some 10 to 20 million years ago. In a 2000 review on the worldwide distribution of psilocybin mushrooms, Gastón Guzmán and colleagues considered these distributed among the following genera: "Psilocybe" (116 species), "Gymnopilus" (14), "Panaeolus" (13), "Copelandia" (12), "Hypholoma" (6), "Pluteus" (6) "Inocybe" (6), "Conocybe" (4), "Panaeolina" (4), "Gerronema" (2), "Agrocybe" (1) and "Galerina" (1). Guzmán increased his estimate of the number of psilocybin-containing "Psilocybe" to 144 species in a 2005 review. Many of these are found in Mexico (53 species), with the remainder distributed in Canada and the US (22), Europe (16), Asia (15), Africa (4), and Australia and associated islands (19). In general, psilocybin-containing species are dark-spored, gilled mushrooms that grow in meadows and woods of the subtropics and tropics, usually in soils rich in humus and plant debris. Psilocybin mushrooms occur on all continents, but the majority of species are found in subtropical humid forests. "Psilocybe" species commonly found in the tropics include "P. cubensis" and "P. subcubensis". "P. semilanceata", considered the world's most widely distributed psilocybin mushroom, is found in Europe, North America, Asia, South America, Australia and New Zealand, although it is absent from Mexico. The effects of psilocybin mushrooms come from psilocybin and psilocin. When psilocybin is ingested, it is broken down to produce psilocin, which is responsible for the psychedelic effects. Psilocybin and psilocin create short-term increases in tolerance of users, thus making it difficult to abuse them because the more often they are taken within a short period of time, the weaker the resultant effects are.