Plastid rbcL sequence data show Dialypetalanthus to be a member of Rubiaceae

Dialypetalanthus fuscescens Kuhlm., endemic to Amazonia, has been treated as the sole member of Dialypetalanthaceae Rizzini & Occhioni. Various affinities have been suggested, but its phylogenetic position has remained unclear due to the unique combination of characters indicating an affinity with Rubiaceae (e.g. opposite leaves, interpetiolar stipules and an inferior ovary), in which family it was originally placed, or Myrtales (free petals and numerous stamens). Analysis of rbcL sequence data indicates that Dialypetalanthus is a member of Rubiaceae sensu stricto and falls in Ixoroideae sensu lato sensu Bremer with relatively strong bootstrap support (83%). Within the subfamily, Dialypetalanthus falls with a group of other neotropical taxa, but this position is not well supported. In the successively weighted trees Dialypetalanthus fell in a clade with the New World taxa Calycophyllum, Capirona, Condaminea, Hippotis, Pentagonia and Pogonopus. However, this clade received bootstrap support of <50%. On the basis of these data we recommend inclusion of Dialypetalanthus in Rubiaceae, but data for other loci and further morphological analysis will be required before its exact relationships can be determined.