Updated taxonomy appears in parentheses.
numerous. However, extensive illegal collecting of plants occurred when a few individuals from eastern Europe learned where they grew, and some local villagers discovered that the plants could be sold and charged visitors for admission to the sites. Although the local villagers naturally resented efforts by conservationists to protect the populations and some illegal collectors were apprehended by Mexican authorities, the devastation of some sites continued. Artificially propagated material of both species is now available in the market, which has led to a reduction in the pressure on the wild populations. Ironically, the seeds and plants used as the source of this artificially propagated material were illegally removed from Mexico. This experience with A. hintonii and G. mexicana has created an interesting dilemma among hobbyists who have ethical concerns about the conservation of cacti. Artificially propagated plants may be purchased, but they are derived from illegally collected stock. However, these plants are also reducing the pressure to collect material from wild populations.
In 1980 the IUCN—The World Conservation Union (a nongovernmental organization created in Switzerland in 1948) established criteria and categories of threat for assessing extinction risks to species. An improved set of criteria and categories of threat was adopted in 1994, which were later used to assess some of the species that were listed in the 1996 IUCN Red List of Threatened Animals and the 1997 IUCN Red List of Threatened Plants. The latter publication lists 33,798 species as threatened, approximately one-eighth of the world's total vascular plants (Walter and Gillett 1998). The Red List has 581 cactus species, approximately 35% of the total number of species in the family. Probably this is a fairly accurate estimate of the conservation threat to the family.
Both category definitions and the criteria by which they are determined have been controversial, so a further revision of the categories is currently under way (IUCN/ SSC Criteria Review Working Group 1999). A system that can be readily used on plant populations is needed, as the present IUCN categories of threat are difficult to apply unless extensive fieldwork is undertaken. The following are the proposed new categories of threat: (1) Extinct—no organisms exist; (2) Extinct in the Wld—organisms still exist but no longer in the wild; (3) Critically Endangered—facing an extremely high risk of extinction in the near future; (4) Endangered— not critically endangered but facing a very high risk of extinction in the wild in the near future; (5) Vulnerable—facing a high risk of extinction in the wild; (6) Near Threatened—do not qualify as threatened but may become so in the near future; (7) Least Concern—do not qualify for any of the above categories. The criteria are based on the evaluation of populations of organisms and a projection of their probable future, but data are often simply insufficient to classify the organism into one group or another. This is particularly true of the cacti, for few detailed, long-term studies have been carried out, underscoring one of the highest priorities for cactus conservation.
Cacti have long been—and continue to be —used by Native Americans in both North and South America. Though their use as food sources has decreased with the improvement of transportation and Native Americans' par-
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