A cladistic analysis and systematic revision of 2 primarily neotropical mite genera, Tropicoseius Baker & Yunker and Rhinoseius Baker & Yunker (Mesostigmata, Ascidae, Melicharini), are presented. The 2 genera and 5 of their species are redescribed, and 11 species of Tropicoseius and 1 species of Rhinoseius are described as new. A key to species of the 2 genera is given. The genera Tropicoseius and Rhinoseius form a monophyletic lineage, of which the sister group appears to be the genus Xanthippe Naskrecki and Colwell. Mites of the genera Tropicoseius and Rhinoseius feed and reproduce within the inflorescences of hummingbird-pollinated plants. Host plant specificity and fidelity is very high. A posteriori mapping of host plant affiliations on the cladogram reveals a striking pattern of origin and radiation for these mites, with 1 clade (Rhinoseius) in dicotyledonous groups of the tropical highlands, and a gradual evolutionary shift within the sister clade (Tropicoseius) to lowland habitats and monocotyledonous hosts.