Phylogeny of the Stachys coccinea (Lamiaceae) complex based on molecular and morphological data

One of the largest genera within the Lamiaceae, Stachys, is in extreme need of taxonomic revision due to its demonstrated phylogenetic polyphyly. Among the New World Stachys, a group of seven species belonging to the Stachys coccinea complex is widely distributed in Mexico, where four of the species in this complex are considered endemic. The members of this complex are characterized by having large and red, orange, or purple corollas. The observed morphological variation, however, may insufficiently circumscribe this number of species, and an assessment combining the use of morphological and molecular data is needed. Here, we evaluated the circumscription of the Stachys coccinea complex and relationships among its members using phylogenetic analyses of chloroplast (cp) DNA sequence data and numerical analysis applied to morphological data. We found that morphological variation in this complex insufficiently circumscribed members of the complex, possibly caused by plasticity of diagnostic morphological characters. In addition, the utilized cpDNA regions, which are commonly used in plant phylogenetic reconstruction (trnL intron, trnL-F spacer, and rps16 intron sequences), render relationships among most of the species in the complex unresolved. We propose that the Stachys coccinea complex be recircumscribed, reducing the number of members to three species: Stachys coccinea, S. lindenii, and S. albotomentosa, keeping the original circumscription of these species and including S. pacifica, S. manantlanensis, S. torresii, and S. jaimehintonii as varieties of S. coccinea.