The challenging Lippia sect. Goniostachyum (Verbenaceae) revisited: Taxonomic, nomenclatural, and distributional updates

Abstract

Lippia sect. Goniostachyum, distributed across the Americas, is a monophyletic group primarily distinguished by spikes with tetrastichous floral bracts. Previous taxonomic studies recognized five to seven taxa, including both species and varieties. However, the taxonomy of the section remains problematic, with unclear boundaries between taxa and frequent misidentifications. In this context, we present a revision of Lippia sect. Goniostachyum, based on the analysis of a broad set of specimens and morphological characters, consequently recognizing nine species. The taxonomic updates encompass the description of Lippia discolor as a new species, new synonymizations under Lippia origanoides, reinstatement of Lippia palmeri, and the redelimitation of the Lippia stachyoides complex. Previously, this complex comprised three infraspecific taxa (Lippia stachyoides var. guajajarana, var. martiana, and var. stachyoides); however, it is redefined to include four distinct species: Lippia guajajarana, Lippia martiana, Lippia pohliana, and Lippia stachyoides. Detailed descriptions, illustrations, an identification key, maps, and notes on taxonomy and distribution are provided to distinguish each species. We also highlight the remarkable morphological variation in Lippia origanoides, a species widely used in traditional medicine and renowned for its pharmacological potential in several studies, which still raises concerns regarding its taxonomic delimitation. Nomenclatural updates include lectotypes designation for Lippia candicans and Lippia schomburgkiana, second-step lectotypification for Lippia polycephala, Lippia polycephala var. aemilii and Lippia sidoides f. flaccida, a neotype for Lantana origanoides, and second-step neotypification for Lippia elegans and Lippia salviaefolia.