Phylogenetic relationships within the tropical clade of Orobanchaceae

The tropical clade of Orobanchaceae contains approximately forty genera, typically with fewer than ten species each, and contributes significantly to the variation in floral morphology found within the family. Despite the economic importance of this clade, which contains three of four most important genera of crop parasites within the family, it has been under-sampled in previous phylogenies. We tested the monophyly of the tropical clade and its major genera using DNA sequences from the nuclear (internal transcribed spacer) and plastid (rpl16, trnT-L) genomes. The tropical clade was strongly supported as monophyletic in all analyses, and four main clades were recovered. The earliest diverging lineage from the remainder of the tropical clade is comprised of the shrubby genera Asepalum and Cyclocheilon, previously placed within Cyclocheilaceae. The atypical holoparasitic Alectra alba was shown to belong within the primarily holoparasitic Harveya, and the hemiparasitic Harveya obtusifolia was shown to belong to an otherwise holoparasitic lineage within Harveya. Both New World Melasma species were included here for the first time, and these were shown to be more closely related to the Neotropical hemiparasitic Escobedia than the African Melasma lineage. These results support a previous study recognizing Nesogenes within the tropical clade of Orobanchaceae rather than the separate family Nesogenaceae.