Molecular phylogenetics suggest Osmiopsis (Asteraceae) could be a rare inter-subtribal hybrid genus on Hispaniola

Abstract

Osmiopsis (Asteraceae, Eupatorieae) is endemic to Hispaniola and one of the seven genera of subtribe Praxelinae. When Osmiopsis was established in 1975, the authors hypothesized it was a hybrid and proposed Chromolaena (subtribe Praxelinae) and Koanophyllon (subtribe Critoniinae) as putative parent genera. To clarify its origin, a phylogenetic investigation of subtribe Praxelinae, reconstructed within a matrix of 80 genera/202 species of tribe Eupatorieae (43% of genera/8% of species sampled, based on an estimated 187 genera/2500 species) was performed. An ILD test showed significant incongruity between the nuclear and chloroplast trees ( p = 0.001). Based on Bayesian analysis of ITS, O. plumieri emerged in a strongly supported clade (PP = 0.98) of 23 species of Critoniinae, closely allied to six Koanophyllon species. Based on Bayesian analysis of ndh F, O. plumieri emerged in a strongly supported clade (PP = 1) of 20 species of Praxelinae with Chromolaena , Praxelis and three other genera. These results suggest Osmiopsis may be a hybrid between Chromolaena and Koanophyllon . Osmiopsis shares with Koanophyllon : infundibuliform corolla with a cylindrical base, triangular corolla lobes and anther appendages wider than longer. Osmiopsis plumieri shares with Chromolaena and Praxelis : semi-scandent habit and deciduous involucral bracts. As far as we are aware, this is the first case of a possible inter-subtribal nothogenus in the Asteraceae. Koanophyllon has more Caribbean island endemics than any other genus in the Asteraceae. This raises the question if hybridization has played a significant role in the diversification of the Caribbean flora, as has been shown in species-rich genera from volcanic archipelagos. Taxonomically, it raises the question if sister subtribes Praxelinae and Critoniinae should be united or re-circumscribed.

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