Molecular Phylogeny of Waltheria L. (Malvaceae, Byttnerioideae) Supports the Recognition of Stegowaltheria as a Distinct Genus

The phylogenetic relationships of Waltheria (Malvaceae) species were investigated, testing its monophyly and infrageneric classification. Approximately half of the genus was sampled, including its two sections, as well as 10 species from three sections of its sister genus Melochia. Phylogenetic inferences were based on Bayesian inference and maximum likelihood analyses of plastid (matK, trnL-F) and nuclear (nrITS) markers. The analyses recovered Waltheria s.l. as non-monophyletic, with Melochia species nested within it. Notably, species of W. sect. Stegowaltheria form a strongly supported sister clade to Melochia. These results indicated the need for taxonomic changes to restore monophyly, and Stegowaltheria was elevated to generic rank, as this required only three new combinations, which are also provided. The new genus is recognized by clear diagnostic features, including the presence of simple trichomes on the branches, stipule shape, capsules with operculate dehiscence, and verrucose seeds. This study contributes to the systematics of Hermannieae and proposes a revised taxonomic circumscription based on molecular and morphological evidence.