Morphology and molecules support the new monotypic genus Parainvolucrella (Rubiaceae) from Asia

Parainvolucrella R.J. Wang, a new monotypic genus for P.scabra (Wall. ex Kurz) M.D.Yuan & R.J.Wang, new combination, is segregated from the Hedyotis-Oldenlandia complex, based on morphological and molecular evidence. Phylogenetically, the new genus is sister to Scleromitrion, from which it differs by a combination of morphological characters: herbaceous habit, terminal inflorescence with subtended leaves, heterostylous flowers, indehiscent fruits and pollen with double microreticulate tectum. A key to the genera of the Hedyotis-Oldenlandia complex in China is provided for further identification.