The phylogeny of Diapensiaceae was investigated by analysis of morphology and molecular data from three genomes; the internal transcribed spacers (ITS) of nuclear ribosomal DNA, rbcL and ndhF from the chloroplast genome, and matR from the mitochondrial genome. Compared to earlier investigations this study is based on a larger data set and has also a larger taxonomic sample that includes representatives of all recognized genera of the family. The results show that Galax is the sister group to all other genera of the family, and that Pyxidanthera is sister to the rest at the next higher node. The relationships between Berneuxia, Diapensia, and Shortia are unresolved. The monophyly of Diapensia is not supported, but has not been tested with molecular data. The monophyly of Shortia is well supported, with S. soldanelloides as sister to the other species. The results indicate that the first diversification in the family occurred in North America with a subsequent diversification of the genera Galax and Pyxidanthera, respectively, and that the ancestor of the remaining genera had an eastern distribution. The small American distribution of Shortia galacifolia is interesting considering the East Asian distribution of its closest relatives, S. uniflora and S. exappendiculata.

Communicating Editor: John V. Freudenstein