Molecular phylogenetics of the hemiparasitic genus Cassytha (Lauraceae)

Haustorial parasitism has evolved in angiosperms at least 12 times, resulting in similar morphological, physiological and genetic changes in these organisms. One such example is Cassytha, the only parasitic genus of Lauraceae. Cassytha is a twining, obligate stem hemiparasite that attaches to its host and uses its haustoria to acquire nutrients and water. The delimitation of species within Cassytha and their phylogenetic relationships remain poorly understood. The last substantial work on this group was conducted by Weber in 1981, using chiefly reproductive morphology to delimit the species. Since then, Cassytha has not been subject to comprehensive taxonomic work. More recent molecular work focused mainly on trying to find the position of Cassytha within Lauraceae, sampling only one-to-few placeholder species. Our current research uses a combination of plastid (trnL–F, rbcL) and nuclear (ITS) sequence regions on an extensive sampling of Cassytha that captures its taxonomic, morphological and biogeographical diversity. Through the extraction and alignment of sequences from over 150 individuals, we have built a nascent tree that comprises nearly all currently accepted Cassytha species. Most species form clades with high bootstrap support, whereas a few require further data to resolve their relationships.