Increased sampling of both genes and taxa improves resolution of phylogenetic relationships within Magnoliidae, a large and early-diverging clade of angiosperms.

Magnoliidae have been supported as a clade in the majority of large-scale molecular phylogenetic studies of angiosperms. This group consists of about 10,000 species assigned to 20 families and four orders, Canellales, Piperales, Laurales, and Magnoliales. Some relationships among the families are still largely debated. Here, we reconstruct the phylogenetic relationships of Magnoliidae as a whole, sampling 199 species (representing ca. 75% of genera) and 12 molecular markers from the three genomes (plastid atpB, matK, trnL intron, trnL-trnF spacer, ndhF, rbcL; mitochondrial atp1, matR, mtSSU, mtLSU; nuclear 18s rDNA, 26S rDNA). Maximum likelihood, Bayesian and maximum parsimony analyses yielded congruent trees, with good resolution and high support values for higher-level relationships. This study further confirms, with greater levels of support, two major clades in Magnoliidae: Canellales+Piperales and Laurales+Magnoliales. Relationships among the 20 families are, in general, well resolved and supported. Several previously ambiguous relationships are now well supported. For instance, the Aristolochiaceae s.l. (incl. Asaroideae, Aristolochioideae, and Lactoris) are monophyletic with high support when Hydnoraceae are excluded. The latter family was not included in most previous studies because of the lack of suitable plastid sequences, a consequence of the parasitic habit of its species. Here, we confirm that it belongs in Aristolochiaceae. Our analyses also provide moderate support for a sister group relationship between Lauraceae and Monimiaceae. Conversely, the exact position of Magnoliaceae remains very difficult to determine. This study provides a robust phylogenetic background to address the evolutionary history of an important and highly diverse clade of early-diverging angiosperms.