The generic boundary of the broadly defined Acanthophyllum s.l., the third-largest genus of the tribe Caryophylleae (Caryophyllaceae), has been a subject of taxonomic confusion. Acanthophyllum s.l. now includes five minor genera previously recognized as independent. Among these small genera, the inclusion of Allochrusa, Ochotonophila, and Scleranthopsis within Acanthophyllum s.l. was confirmed by previous molecular studies, while the positions of Diaphanoptera and Kuhitangia remained uncertain. We have performed an updated molecular study of Acanthophyllum s.l. including an increased sampling of the genera and sections assigned to this group, using intron sequences of the chloroplast gene rps16 and nuclear ribosomal internal transcribed spacer (ITS) sequences. Cyathophylla, Heterochroa, and Saponaria were chosen as outgroups for performing phylogenetic analyses using maximum likelihood and Bayesian methods. The present results suggest that, in addition to the genera mentioned above, both Diaphanoptera and Kuhitangia should also be synonymized within Acanthophyllum. Sections Diaphanoptera, Kuhitangia and Pseudomacrostegia are introduced as new infrageneric taxa within Acanthophyllum. Our results also indicate that some annual species of Saponaria are closely related to Acanthophyllum.

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