Figure 1.

Phylogenetic tree of Nearctic and Palearctic oak gall wasps represented by the partitioned 75% complete data matrix. Clades have been collapsed to the species, or rarely genus, level (see Fig. S3 for the expanded tree). Tips with more than one species name indicate apparent polyphyly or the closing of life cycles (see File S2). All nodes have 100% bootstrap support, except for those indicated with black (<100%) or white (<80%) stars. Clades shaded in gray comprise Palearctic species. The grid to the right of the tree indicates the association of each gall with an oak section (or two sections, in the case of the alternating‐host Palearctic Andricus clade). The cladogram above the right‐hand grid illustrates the relationship among the oak sections: C = Cerris, L = Lobatae, P = Protobalanus, V = Virentes, Q = Quercus. (1) = from galls on chestnut (Castanea); (2) = from galls on Chrysolepis. Dark circles, superficially resembling galls, on some branches of the phylogeny indicate changes in host tree section, assuming an ancestral association with oaks in subgenus Quercus, section Quercus as suggested by Ancestral State Reconstruction (Fig. S6).