Evolutionary diversification of gall morphology and host plant use in willow-galling sawflies. The tree is according to a Bayesian phylogenetic analysis of 1 528 bp of DNA sequence data from two mitochondrial genes (see Methods), numbers above branches show posterior probabilities of clades. Host plants are indicated after the sawfly species names. Ancestral gall types were reconstructed using Accelerated transformations parsimony optimization (the ancestral state of the Euura clade is equivocal, but it was probably shoot galling ). The pie diagram at the node between Euura and their sister group shows the relative likelihood of different gall locations as reconstructed by maximum likelihood.