Towards a better understanding of the Chromolaena congesta complex (Asteraceae, Eupatorieae): updated synopsis with taxonomic novelties

Taxonomic treatments for species complexes are a continuing challenge, in which new information and further questions are constantly being formulated. Regarding the Chromolaena congesta complex, recent studies with morphological data, geographic distribution and climatic niche have shed light on needed changes in the recognition and identification of some species. This paper presents a synopsis and an identification key of the species complex, which now consists of 11 taxa. Taxonomic novelties presented in this paper include a new combination for Eupatorium caaguazuense var. nervosum, re-established from the synonymy of C. squarrulosa and now treated as a distinct species, and the description of a cryptic new species from Southern Brazil with unique morphological traits. Furthermore, we propose the synonymy of C. xylorhiza under C. ascendens and provide updated information regarding distribution and evaluation of conservation status for each species. Finally, we included some insights on further studies to be conducted in the C. congesta complex to answer questions that still hamper the taxonomy and systematics of these species.