Acanthochronology is the study of cactus spines or Euphorbia thorns grown in time ordered sequence (i.e. in series). Physical, morphological or chemical characteristics and information about the relative order or absolute age of the spines or thorns is used to study past climate or plant physiology. The first peer-reviewed article to present and explain an isotope spine series was from a saguaro cactus in Tucson, Arizona. This and other work shows that radiocarbon and isotope time-series derived from spines can be used for demographic or palaeoclimate studies.