Phylogenetic and ecological signals in the wood of Spathelioideae (Rutaceae)

Abstract

Subfamily Spathelioideae of Rutaceae constitutes a well-supported early branching clade of eight small woody genera that were formerly assigned to five different Sapindalean/Rutalean families. This study brings together detailed wood anatomical information on all eight genera (for four the wood anatomy is described for the first time in detail). Wood anatomy strongly supports the inclusion of all Spathelioid genera in Rutaceae and underpins the molecular phylogeny with a set of interesting apomorphies at different nodes of the cladogram. The wood anatomy of Cneorum tricoccon with its semi-ring porosity, dendritic vessel pattern, vascular tracheids and helical vessel wall thickenings stands out in Spathelioideae. This wood anatomical syndrome is hypothesized to be due to adaptive evolution for hydraulic safety and efficiency of this species in a typical Mediterranean climate, where similar syndromes have evolved in many unrelated clades of woody dicots. In at least six unrelated genera of Rutaceae outside Spathelioideae from Mediterranean or cool temperate and montane climates, the syndrome has also evolved in presumably parallel, adaptive evolution.