Figure 1. Framework for documenting homoploid hybridization speciation employed Wang et al. (2021) for Ostryopsis intermedia(hazel-hornbeam) and subsequently applied to other species. Satisfying the three criteria for establishing homoploid hybrid speciation (Schumer et al., 2013): ( A) Demographic modelling and phylogenomic analyses providing evidence for previous admixture in hybrid species; (B) Quantifying and inferring reproductive isolation between the hybrid species and parents, including example from Heliconiusbutterflies in which the combination of parental wing patterns in the hybrid led to premating isolation with its parents (Mavárez et al. 2006); and (C) Identifying positively selected genes (PSGs) associated with reproductive barriers, determining the ancestry of the candidate genes ,and performing functional validation of these genes; (D) Applying this framework to other four examples of homoploid hybrids, includingCarpinus cordata (heartleaf hornbeam; a species from sect.Distegocarpus ), Ursus thibetanus (Asiatic black bear),Rhinopithecus brelichi (gray snub-nosed monkey) and Macaca fascicularis (long-tailed macaque; a species from thefascicularis group). Grey arrows show geographic location of homoploid hybrid species.