Pleiacanthus
 Pleiacanthus is a monotypic genus of flowering plants in the aster family containing the single species Pleiacanthus spinosus (formerly Stephanomeria spinosa) which is known by the common name thorn skeletonweed or thorny skeletonweed. It is native to the western United States from Montana and Idaho to southern California and Arizona where it grows in many types of mostly dry habitat from deserts to mountains.