The Praxelinae comprises two genera—Praxelis and Chromolaena—and 19 species in Rio Grande do Sul, the southernmost State of Brazil. This is the first taxonomic treatment of these genera in the state according to their current circumscriptions. Chromolaena squarrosoramosa is formally reported for the first time for the flora of the state. The names C. callilepis and C. paraguariensis are used for the first time to refer to species previously known as Eupatorium polyanthum and E. angusticeps. Eupatorium angusticeps, considered in previous studies endemic to Rio Grande do Sul and probably extinct, is synonymized under C. paraguariensis and has its geographical range extended. Two neglected names, C. elliptica and C. latisquamulosa, are re-established, and C. umbelliformis is synonymized under C. elliptica. Furthermore, C. rhinanthacea is recollected for the first time after 40 years, and C. gentianoides is rediscovered in the state after almost 200 years of the original collection. Identification key and morphological descriptions, as well as distribution maps, field photographs, illustrations and general comments on the biology, ecology and identification of the species are provided.

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Resumo Moquiniastrum, originalmente descrito por Cabrera como uma seção de Gochnatia, após análises moleculares e morfológicas mais detalhadas foi elevado à categoria de gênero. Moquiniastrum diferencia-se de Gochnatia pela presença de ginodioicia, indumento de tricomas com 2-5-raios e capitulescências paniculiformes. Atualmente é constituído por 21 espécies, distribuídas principalmente no Brasil. Pouco se conhece sobre a taxonomia do gênero Moquiniastrum e ainda há escassez de estudos sobre o arranjo sexual das flores no capítulo, necessitando de análises aprofundadas destas estruturas. O objetivo geral deste trabalho foi realizar um estudo taxonômico de Moquiniastrum na Região Sul do Brasil, além de avaliar e enquadrar os táxons em categorias de ameaça de extinção. Este estudo foi realizado através de revisões de herbários e expedições de campo nos três estados da Região Sul do Brasil. Foram encontradas 10 espécies de Moquiniastrum, além de três subespécies de M. polymorphum. São fornecidos chave de identificação para os táxons confirmados, descrições morfológicas, comentários sobre habitats, conservação e períodos de floração e de frutificação das espécies, além de observações taxonômicas e imagens.

The genera Chromolaena Candolle (1836: 133) and Praxelis Cassini (1826: 261) (Asteraceae: Eupatorieae) were both segregated from Eupatorium Linnaeus (1753: 836) in 1970 (King & Robinson 1970a, 1970b). Despite several taxonomic studies (including new combinations and typifications) since then, there are still countless names that need to be typified. As a result of our ongoing taxonomic treatment of both genera in the state of Rio Grande do Sul, Brazil, we propose here five lectotypes and one neotype in Chromolaena and one lectotype in Praxelis.

The Chromolaena congesta complex (Asteraceae, Eupatorieae) presents a difficult challenge for biodiversity researchers due to the intertwined connections of its species and the difficulty of establishing morphological boundaries. In this study, we aimed to use morphometric analyses to evaluate the delimitation of the taxa belonging to the C. congesta complex, identify informative morphological traits and to understand the identity of several "atypical" specimens morphologically related to the complex. To achieve this, we used cluster and principal component analysis to evaluate 50 morphological traits from a total of 210 specimens throughout the geographic distribution of the species complex. We found support for the recognition of at least six species -Chromolaena ascendens, C. gentianoides, C. hirsuta, C. latisquamulosa, C. rhinanthacea and C. squarrulosa -according to a phenetic species concept and to corroborate the restoration of three species from synonymy. Furthermore, our results provide a morphological recircumscription of C. congesta and C. elliptica and indicate two taxonomic novelties, including a new combination and a new species. Despite the answers provided by morphology, many taxonomic issues remain to be solved, and further studies with other types of evidence should be carried to contribute towards a more stable classification.