A New Heterophyllous Spermacoce Species (Rubiaceae) from the Marungu Highlands, Democratic Republic of the Congo

Spermacoce heteromorpha Dessein (Rubiaceae, Spermacoceae) is newly described and illustrated. It grows on the Marungu highlands of the Democratic Republic of the Congo (D.R. Congo) at altitudes of 1800 to 1900 m. The species resembles the Tanzanian Spermacoce taylorii Verdcourt, from which it mainly differs in having terminal inflorescences, only slightly exserted anthers, and densely pubescent stems. Moreover, Spermacoce heteromorpha features marked heterophylly, with long leaves at the plant’s base and much shorter cauline leaves, a type of heterophylly rarely observed in Spermacoce or in the Rubiaceae as a whole. The finding of this species exemplifies the unique floristic richness of this underexplored part of D.R. Congo.