Molecular phylogenetic study of Argyreia (Ipomoeeae: Convolvulaceae) and implications for its systematics

The genus Argyreia (Convolvulaceae) comprises 142 species distributed in tropical Asia and Madagascar and is part of the tribe Ipomoeeae in which all members possess spiny pollen. It is one of the most species-rich genera within the Convolvulaceae, after Ipomoea, Cuscuta, and Convolvulus, and contains economically important species (e.g., Argyreia nervosa). Unlike the other genera, it remains under-represented in molecular phylogenetic studies and still has not been fully monographed. The genus shows high morphological diversity and variation, which sometimes cause confusion in species delimitation, especially in species complexes. In this present study, the nuclear internal transcribed spacer (ITS) region and three plastid (matK, rps16, and trnL-trnF) regions were sequenced or retrieved from GenBank for 179 accessions of Argyreia covering 64 species, the largest sampling of the genus so far, and another 69 Ipomoeeae taxa from Astripomoea, Ipomoea, Lepistemon, Lepistemonopsis, Rivea, and Stictocardia. Our phylogenetic analyses recovered eight clades within Argyreia, with strong support. No morphological distinction was recognized for any of the clades, except for Clade G, in which all members have dense silvery hairs on abaxial leaf surfaces. Species complexes in the genus were also explored, with some species requiring re-circumscription.