Extinction threat in the Pedilanthus clade (Euphorbia, Euphorbiaceae), with special reference to the recently rediscovered E. conzattii (P. pulchellus).

The type locality of the slipper spurge Euphorbia conzattii has been in doubt because the 1917 type is a mixed collection with vague label data. In recent field work, the species was found on Cerro Espino, Pochutla District, Oaxaca, Mexico. We used the Method for Evaluation of Risk of Extinction for Mexican Wild Species (MER), required to protect a species under Mexican law, to assess the conservation status of E. conzattii and found it to be endangered. We discuss the mixture in the type of this species with E. calcarata and present an updated description and an illustration of E. conzattii. Preliminary MER assessments of the other Mexican Pedilanthus clade species show two species to be extinct (E. cyri, E. dressleri) and four threatened (including E. colligata, E. finkii, E. tehuacana). The remaining eight have more favorable outlooks. We comment on MER robustness and aspects vulnerable to confusion and offer clarifications. Extinction risk is not distributed evenly throughout the clade, with a subclade of leafy treelets from a variety of habitats having the greatest number of endangered species. Extinction risk is distributed across all Pedilanthus-clade habitats; the strongest association noted is that both species from moist highlands are endangered.