Abstract The distribution of dichogamy in Acanthaceae is unknown, yet studies in the genus Justicia from Africa described the occurrence of protandry with staminal movement. A review of the genus suggests African species show protandry with staminal movement but New World species do not. In this study, we test this hypothesis. We also propose that hummingbird pollination led to the loss of this form of dichogamy. We inferred a time-calibrated molecular phylogeny of Acanthaceae and scored species within tribe Justicieae for protandry with staminal movement and pollination syndrome. We used ancestral state reconstruction to determine how many times staminal movement evolved in Justicieae, and tested for correlated evolution between changes in staminal movement and changes in pollination syndrome and geography. We scored a total of 333 species in tribe Justicieae, of which 58 showed protandry with staminal movement and 275 did not. Mapping staminal movement onto the phylogeny revealed multiple origins of this type of protandry, and significantly a loss in the common ancestor of New World ‘justicioids’ with a single regain in the Neotropics. Protandry with staminal movement is common in Old World Justicieae but confirmed to be almost absent in the New World. As Neotropical Justicia are nested in an Old World clade, it is clear they lost protandry with staminal movement and regained it once in the New World. Insect foraging behaviour probably drove the evolution of protandry with staminal movement and hummingbird foraging behaviour probably drove the loss of protandry with staminal movement in this clade. This summary, translated into Spanish, is available in the Supporting Information section (Appendix S1).
Kriebel et al. (2026) studied this question.