A tale of two cacti: studies in Astrophytum asterias and Lophophora williamsii



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Texas A&M University


Astrophytum asterias (star cactus) and Lophophora williamsii (peyote) are sympatric species in the Tamaulipecan thornscrub of South Texas and adjacent Mexico. Peyote has been excavated from two archaeological sites: Shumla Caves, Texas, and CM-79 in Coahuila. We report new radiocarbon dates: a mean of 5195 ???? 20 14C years BP for the Shumla Caves specimens, and 835 ???? 35 14C years BP for the CM-79 specimen. The Shumla Caves specimens were not intact peyote tops, but manufactured effigies thereof. Published data on the geographic ranges of L. williamsii and A. asterias are of varying quality and accuracy. We report the results of extensive research to document extant U.S. populations by county, drawing specific conclusions about where each species currently occurs, where its occurrence is uncertain and where it is unlikely, based on herbarium specimens, verifiable reports in the primary literature and interviews with knowledgeable individuals. Dwindling of populations of peyote is partly due to improper harvesting, namely cutting off the top of the plant so deeply below ground level that the plant is unable to regenerate new stems, and consequently dies. We describe the anatomy of the cactus shoot (stem) and root, and suggest how this new knowledge can be utilized to determine "how deep is too deep" to cut if harvesting of peyote is to be done sustainably. We report the first population genetics study on endangered A. asterias, with five microsatellite markers in populations sampled at four locations in South Texas. A battery of tests and measurements indicated that in most populations heterozygosity was high, F-statistics were low, and Nm was >1. With one exception, these populations appear not to be undergoing excessive inbreeding, despite small population sizes. Data from two L. williamsii microsatellite loci are presented. L. williamsii, which reproduces autogamously, exhibits a single homozygous genotype within a given population. West Texas L. williamsii plants differ from South Texas plants in the identity of the single allele (or single genotype) at each locus. The ability of microsatellite markers to separate West Texas from South Texas plants suggests utility of microsatellites for infraspecific taxonomic studies in Lophophora.