Integrative Taxonomic Analyses Sheds Light on Three Historically Disputed American Spermacoce Species, and a Key to the American Species of Spermacoce (Spermacoceae, Rubiaceae)

Abstract

There has been great confusion between Spermacoce glabra, S. riparia, andS. tenuior since their original descriptions. These species can bedistinguished mostly by their seed features. Clustering and principal coordinate analyses (PCoA) were used to scrutinize the formation of hierarchicalnon-overlapping groups strictly according to the degree of morphological similarity. Thirteen characters were scored for 26 herbariaspecimens. The taxonomic identity of these three species is discussed. Redefined descriptions and illustrations are provided, especially for fruit, seed,and pollen characters. A map and a discussion of the updated geographical distribution of these species are included. A table summarizing thedifferent taxonomic concepts in contemporary floristic studies and an identification key to all American Spermacoce species are also provided. Thenew combination Spermacoce affinis (DC.) R.M. Salas is presented here.