Premise: Cytogenetic traits such as an organism's chromosome number and genome size are taxonomically critical and can define angiosperm diversity. Variations in these cytogenetic traits by evolutionary processes such as polyploidization are known to be common, although underexplored in tropical plants. Zingiberaceae is a pantropical monocot family with ~1500 species where cytogenetic characters have often been used to define taxonomic boundaries, but a family-wide synthesis of cytogenetic patterns is absent.

Methods: A time-calibrated Bayesian phylogenetic tree was constructed to test for different models of chromosome number and genome size evolution in Zingiberaceae. We next tested how chromosome number and genome size variations differed with lineage-age, taxonomic diversity, and distributional range at two taxonomic ranks: within the family Zingiberaceae, and in the genus Hedychium using correlations, generalized linear models and phylogenetic least square models.

Key results: The most frequent changes in chromosome number within Zingiberaceae were demi-polyploidization and polyploidization (~57 % of the time), followed by ascending dysploidy (~27 %). The subfamily Zingiberoideae showed descending dysploidy at its base, while Alpinioideae showed polyploidization at its internal nodes. Although chromosome counts and genome sizes did not corroborate with each other, suggesting that they are not equivalent, at both taxonomic ranks, higher chromosome number variations and higher genome size variations were associated with higher taxonomic diversity and wider biogeographic distribution.

Conclusions: Within Zingiberaceae, multiple incidences of polyploidization were discovered, and these cytogenetic events appear to have impacted the morphology, decreased genome sizes, and increased taxonomic diversity, distributional range and invasiveness of plants within this family.