Morphological and phylogenetic investigations for several cryptic ant-plants found in Callicarpa (Lamiaceae) from Borneo

A tropical small tree, Callicarpa saccata, is known to have a symbiotic relationship with ants. It has sac-like structures at the base of the leaves that are inhabited by ants. No other species has been determined to be a myrmecophyte among the ca. 140 species of this genus. However, our recent field investigation discovered that two other species on Borneo ( C. barbata and C. teneriflora ) have hollow stems, which seem to be inhabited by ants. We observed the morphological features of these species in relation to their usage by ants, and became convinced that they are mymecophytic species. The molecular phylogenetic analyses using ITS and chloroplast regions suggest that C. saccata and C. teneriflora are closely related, but the differences in the myrmecophytic features of these species should be noted.