Phylogenetic tree space for species tree ((((A,B),C),D),E), where x and y correspond to the lengths of the oldest and youngest ingroup internal branches, respectively (as shown in Fig. 1a). The region shaded in gray corresponds to the anomaly zone (derived in Degnan and Rosenberg 2006; and shaded in black in Fig. 1b), in which the most common gene tree is AGT (((A,B),(C,D)),E). Dots show the most common simulated gene tree at each tree space coordinate (out of 20,000 trees).