Waltheria marielleae (Byttnerioideae, Malvaceae), a new species from north-eastern Brazil supported by morphological and phylogenetic evidence

Background – Waltheria marielleae is a new species of Malvaceae endemic to north-eastern Brazil that occurs only in the states of Pernambuco and Alagoas, in areas of Atlantic Forest and Caatinga. It is characterized by cinereous leaves, axillary and sessile to subsessile inflorescences, pallid yellow corollas with apically eciliate petals and fan-plumose stigmas. Material and methods – DNA was extracted from leaf tissue and the markers matK, ndhF, and ITS were amplified using universal primers, with PCR products purified and sequenced. Phylogenetic analysis was performed, including DNA sequences obtained from GenBank. Morphological studies were based on the analysis of specimens deposited in seven herbaria and specimens collected in Pernambuco state, Brazil. Results – Waltheria marielleae is morphologically and phylogenetically related to pantropical W. indica and W. ackermanniana, with these three species forming a well-supported clade. Overall, phylogenetic molecular analysis suggests the monophyly of Waltheria, with the two currently proposed sections also being monophyletic, and Melochia as its sister group. The new species is assessed here as Endangered, according to IUCN criteria. In addition, we formally present new occurrences of W. ackermanniana and W. rotundifolia. Conclusion – In this study, a complete morphological description, illustration, distribution map, and phylogenetic tree are provided for Waltheria marielleae. This species is compared with morphologically and phylogenetically related species (W. ackermanniana, W. indica, and W. rotundifolia) and an identification key to the species occurring in Alagoas and Pernambuco is provided.