Haageocereus tenuis is a prostrate cactus restricted to a small area of 2 km2 near the city of Lima, Peru. The species is triploid and propagates mainly through stem fragmentation. In addition, propagation via agamospermy is documented and adventitious embryony is also inferred as a mechanism. Although seedling recruitment has not been observed in nature, we have shown that asexually produced seeds are viable. About 45 adult individuals, plus 9 individuals obtained from seeds, were sampled and 5 microsatellite markers were used to assess genetic variability. Microsatellite analysis confirms that individuals from the only existing population are genetically identical and that the population likely represents a single clone. The absence of mutations in any individual, even in highly variable microsatellite loci, may indicate that the species is also of recent origin. Other prostrate species of Haageocereus are suspected to be occasional apomicts. This phenomenon has significant implications for the evolutionary biology and ecology of Haageocereus and other clonal Cactaceae. © 2012 The American Genetic Association. All rights reserved.