Phylogeographic structure across one of the largest intact tropical savannahs: Molecular and morphological analysis of Australia’s iconic frilled lizard Chlamydosaurus kingii

•Genetic data from five loci show three shallow genetic clades within frilled lizards.•Clades are broadly consistent with clinal variation in frill color.•Data from 279 specimens shows only subtle morphological differentiation between clades.•Biogeographic patterns are consistent with other taxa in the Australian monsoon tropics.•Extremely low divergences suggest recent gene flow between, and extensive gene flow within, clades.