Species delimitation in Lippia section Goniostachyum (Verbenaceae) using the phylogenetic species concept

Abstract

Lippia section Goniostachyum comprises plants distinguished by their numerous axillary florescences (three to six, sometimes up to nine) and tetrastichous floral bracts. Species of section Goniostachyum occur in the Neotropics, from Mexico to northern Argentina. Delimitation of the species grouped under Goniostachyum has remained unclear. Forty-one names exist under this section, but only c. eight to ten names have been used frequently. To resolve the taxonomy of this group, a modified population aggregation analysis, based on the phylogenetic species concept, was employed. As a result, Goniostachyum is here circumscribed to only four species: L. grata, L. origanoides, L. sericea and L. stachyoides. These species are supported by different combinations of three characters of the 13 qualitative attributes analysed: canescent sericeous pubescence, frondose or frondose-bracteose inflorescences and free or fused florescence apical bracts. Two varieties based on significant differences among quantitative characters are recognized: L. stachyoides var. stachyoides and L. stachyoides var. martiana comb. nov. Fifteen lectotypifications and four neotypifications are proposed.