The wood anatomy of the polyphyletic Icacinaceae s.l., and their relationships within asterids

TLDR: In this paper, the authors used maximum parsimony and Bayesian analyses using molecular data and combined anatomical-molecular data to show that Icacinaceae s.str. are not monophyletic and their closest relatives remain unclear.

Abstract: Wood samples from 53 species belonging to 41 genera of the Icacinaceae s.l. are investigated using light and scanning electron microscopy. The traditionally circumscribed Icacinaceae fall apart into four segregate families that are clearly nested within asterids, i.e., Icacinaceae s.str. (near or in Garryales), Cardiopteridaceae and Stemonuraceae (both Aquifoliales), and Pennantiaceae (Apiales). From a wood anatomical point of view, these families cannot easily be distinguished from each other. However, some features such as vessel distribution, perforation plate morphology, size and arrangement of vessel pits, fibre wall thickness, and the occurrence of cambial variants can be used to assign various species to one of the four families. The wood structure of the four segregate families is in general agreement with their suggested putative relatives, but the occurrence of lianas versus erect trees and shrubs is a confusing factor in getting clear phylogenetic signal from the wood structure. Maximum parsimony and Bayesian analyses using molecular data and combined anatomical-molecular data show that Icacinaceae s.str. are not monophyletic, and their closest relatives remain unclear. The combined analyses provide moderate support for a clade including Cassinopsis, the Apodytes-group, the Emmotum-group (all Icacinaceae s.str.), and the genus Oncotheca. This clade is situated at the base of lamiids and may be closely related to Garryales. The remaining lineage of Icacinaceae s.str., the Icacina-group represented by many climbing taxa exhibiting cambial variants, is strongly supported and might be sister to the rest of lamiids.