Phylogeny and origins of holoparasitism in Orobanchaceae.

PREMISE: Orobanchaceae are a family of angiosperms that range from fully autotrophic and free-living to completely heterotrophic and dependent on their hosts (holoparasites). Most of the ca. 2060 species are hemiparasites that photosynthesize throughout all or part of their life cycles. Certain family members are ecologically important due to direct impacts on community biomass and diversity, plant-herbivore interactions, and nutrient cycling. Other members are among the most economically damaging weeds in the world. Multiple trophic transitions within this family make it ideal for studying molecular evolutionary and physiological changes that accompany the evolution of parasitism. • METHODS: To establish a phylogenetic framework for such work, we substantially increased taxonomic sampling at loci for which a significant amount of data already existed (nuclear ITS and PHYA, plastid matK and rps2) and added data from the low-copy nuclear locus, PHYB. • KEY RESULTS: The data provide strong support for relationships among six major clades and for the position of Brandisia hancei Hook. f. The positions of Boschniakia himalaica Hook. f. & Thomson, Centranthera cochinchinensis (Lour.) Merr., Mannagettaea hummelii Harry Sm., and Pterygiella nigrescens Oliv. are confirmed or suggested for the first time. • CONCLUSIONS: There is a single origin of parasitism, and from within the hemiparasites, holoparasitism has originated three times. Moving from the base to the tips of the Orobanchaceae tree, the successive major splits within the parasitic clade are: Cymbarieae + the rest; Orobancheae + the rest; Brandisia + the rest; Rhinantheae + the rest; and Pedicularideae + Buchnereae.

Phylogeny of the parasitic plant family Orobanchaceae inferred from phytochrome A.

Partial sequences of the nuclear gene encoding the photoreceptor phytochrome A (PHYA) are used to reconstruct relationships within Orobanchaceae, the largest of the parasitic angiosperm families. The monophyly of Orobanchaceae, including nonphotosynthetic holoparasites, hemiparasites, and nonparasitic Lindenbergia is strongly supported. Phytochrome A data resolve six well-supported lineages that contain all of the sampled genera except Brandisia, which is sister to the major radiation of hemiparasites. In contrast to previous plastid and ITS trees, relationships among these major clades also are generally well supported. Thus, the robust phylogenetic hypothesis inferred from the PHYA data provides a much better context in which to evaluate the evolution of parasitism within the group. Ninety-eight species of Orobanchaceae, representing 43 genera, are included and Brandisia, Bungea, Cymbaria, Esterhazya, Nesogenes, Phtheirospermum, Radamaea, Siphonostegia, and Xylocalyx are confirmed as members of Orobanchaceae. The earliest diverging lineage of hemiparasites is identified for the first time; it contains Bungea, Cymbaria, Monochasma, Siphonostegia, and the monotypic Schwalbea, which is federally endangered. This basal clade is marked by the presence of two novel introns. A second, apparently independent gain of one of these introns marks a clade of largely European taxa. There is significant rate heterogeneity among PHYA sequences, and the presence of multiple PHYA in some taxa is consistent with observed ploidy levels.

Phylogenetic relationships among Strobilanthes s.l. (Acanthaceae): evidence from ITS nrDNA, trnL-F cpDNA, and morphology.

Chloroplast trnL-F sequence data, nuclear ribosomal internal transcribed spacer (ITS) sequence data, and morphology were used to analyze phylogenetic relationships among members of the subtribe Strobilanthinae. Parsimony and maximum likelihood analyses of trnL-F indicate that the Strobilanthinae are a monophyletic group. While parsimony analysis of ITS recovers a nonmonophyletic subtribe, maximum likelihood analysis of ITS corroborates results from trnL-F and suggests that systematic error is impacting on ITS parsimony analysis. A combined ITS and trnL-F analysis strengthens the signal and also recovers a monophyletic subtribe. All analyses indicate that Hemigraphis, Sericocalyx, and Strobilanthes are nonmonophyletic. With one exception, all morphological characters included in a combined ITS and morphological analysis are homoplastic. The prospect for a new informative generic classification of the Strobilanthinae aiming to recognize and diagnose only monophyletic groups is considered. While some groups can be diagnosed, adequate diagnosis of the majority of groups remains problematic. Consequently, a single expanded genus Strobilanthes sensu lato is proposed at the level of the well-supported and monophyletic Strobilanthinae.