Leaf anatomical features and their implications for the systematics of dragon's blood, Croton section Cyclostigma (Euphorbiaceae)

Establishing species limits in clades in Croton using characters from external morphology and common molecular markers has proved cumbersome, especially in Croton section Cyclostigma, a group of 50 Neotropical arborescent species commonly known as dragon's blood. Given this, we explored leaf and shoot apex anatomical characters for their utility in distinguishing species or groups of species in this section. We analysed 90 specimens belonging to section Cyclostigma and 14 specimens from related groups (sections Adenophylli, Cupreati and Sampatik), recording and describing 45 qualitative leaf characters. These characters were assembled into a matrix and analysed using statistical clustering methods based on similarity. Our results show that trichomes are one of the most diverse and variable anatomical features among the studied specimens. Novel anatomical features for Croton include the presence of a hypodermis and two previously unreported types of non-glandular trichomes. Although we did not detect a single anatomical character uniting section Cyclostigma, combinations of anatomical characters were useful to establish species limits and taxonomic identities within this section.ACF thanks FAPEMIG for the scholarship in Brazil during her doctoral degree, the CAPES foundation through PDSE (99999.009518/2014-02) supporting her stay at the Real Jardín Botánico-CSIC (Madrid) and the Programa de Capacitação Institucional (MPEG/MCTI) for the current CNPq research grant. RMSAM was supported by CNPq (477867/2013–8). RR was supported by a Visiting Scholar Fellowship to Brazil funded by FAPEMIG (CRA-BPV-00043-14) and CNPq research grant (477867/2013–8). Additional support was provided by Centro de Ciências Ambientais Floresta Escola (SECTES/UNESCO/HidroEX/FAPEMIG). We are grateful to two reviewers and the associate editor for their valuable suggestions and critical comments to earlier versions of this manuscri