Palm stem anatomy: phylogenetic or climatic signal?

The diversity of palm stem anatomy is now well known, but no study has dealt with the influence of climatic conditions. Here, we conducted research in order to establish whether this diversity follows a phylogenetic pattern and/or whether it is correlated with climatic factors. To answer this question, 98 genera and 137 species that cover the five palm subfamilies were sampled. Anatomical descriptors and measurements of vessel diameter were used in multiple correspondence analyses (MCAs) and hierarchical clustering in order to analyse correspondences between anatomy and climate [tropical rain forest (TRF) palms vs. palms growing in a climate with a dry period]. Qualitative anatomical descriptors were plotted on a recent phylogenetic tree. MCA outlined correlations between: (1) one-vessel palms and TRF palms; (2) two-vessel palms and 'dry period' palms; (3) small vessel diameter (< 144 μm) and 'dry period' palms; and (4) large vessel diameter (> 183 μm) and TRF palms. From phylogenetic analyses, Arecoideae (and, to a lesser extent, Calamoideae) is defined as the one-vessel subfamily, Coryphoideae as the two-vessel subfamily and Ceroxyloideae with three to several vessels per fibrous vascular bundle. Palm stem anatomy is thus correlated with climate (TRF vs. non-TRF), but also shows a phylogenetic signal. Therefore, it suggests that the diversification of Arecoideae and Coryphoideae coincided with the beginning of their ecological dominance.