Providing tools for the reassessment of Eupatorieae (Asteraceae): Comparative and statistical analysis of reproductive characters in South American taxa

Abstract

The Eupatorieae represent nearly 10% of the Asteraceae by including about 187 genera and 2500 species. With close to 116 genera, South America is one of the richest areas of Eupatorieae diversity. The morphological variation of its genera, together with the partly incongruent circumscription of genera and subtribes yielded by morphological and molecular characters make difficult to understand the taxonomy of the tribe. In addition, clustering analyses based on morphological characters have not been carried out to explore to what extent the grouping of species obtained by these studies agrees with those provided by molecular analyses. In order to contribute to the morphological definition of the clades obtained by molecular ongoing studies, the objectives of this study are 1. To describe, characterize, compare, and assess the variability of reproductive characters in representative genera of South American Eupatorieae and, 2. To carry out a clustering analysis using reproductive morphological characters of these taxa. Additionally, we also aim to provide an even terminology of the features to be used by the specialists and detailed drawings of the reproductive structures to help to disentangle the complex morphology of Eupatorieae.A total of 123 species belonging to 42 South American genera and 14 subtribes of Eupatorieae were studied. Twenty-eight characters of involucre, receptacle, corolla, stamen, style, pappus and cypsela were morphologically and anatomically analyzed and compared. All these characters were included in the clustering analyses. The dendrogram was built using UPGMA method. Our work provides a comparative study of reproductive morphology at species level, involving 14 of the 19 subtribes of Eupatorieae. The South American studied species showed a high variability of reproductive characters. According to our statistical results, the representative genera of each Alomiinae, Ayapaninae Critoniinae, Disynaphiinae, Eupatoriinae, and Gyptidinae did not cluster together in the analysis. These outcomes agree with molecular studies that variously found these subtribes out as polyphyletic or paraphyletic. The genera of other subtribes clustered together in our statistical analysis as well as in molecular studies that found these subtribes monophyletic: Adenostemmatiinae, Fleischmanninae, and Mikaniinae. At genus rank, our results found that the sampled species of many genera clustered together, e.g., Mikania, Stevia, Barrosoa, Campoclinium, Ophryosporus, in agreement with molecular studies that found these genera monophyletic. At the same time, the species of some genera that were found para- and polyphyletic in molecular studies were obtained also in different clusters in our study, e.g., Chromolaena, Heterocondylus. In other cases, however, our results do not agree with previous molecular studies, e.g., Kaunia, Praxelis. Interestedly, our statistical analysis showed genera from different subtribes clustering together similarly to that found by molecular studies: e.g., Austrobrickellia and Stomathantes, Malmeanthus close to members of Disynaphiinae. Our results coincide with the molecular studies which obtained Stevia distantly related to Ageratum thus supporting the exclusion of Stevia from Ageratinae. All these findings should be corroborated by the addition of more species to both statistical and molecular analyses. In the light of our results, and despite some potential bias related to the sampling of species and the election and codification of characters, we can conclude that, as in recent molecular studies, the circumscription of many of the traditionally defined subtribes and many genera should be re-evaluated to describe monophyletic entities.