Phylogenetic analyses and perianth evolution in basal angiosperms

Using a compartmentalization approach, we conducted phylogenetic analyses of the basalmost extant angiosperms using sequences from six genes (over 12,000 bp per taxon) from all three genomes (chloroplast-atpB, rbcL; nuclear-18S rDNA, 26S rDNA; mitochondrial-matR, atpA). Trees resulting from parsimony and maximum likelihood analyses of the compartmentalized data are identical. We find strong support (100% for each node) for the earliest-branching angiosperms: Amborellaceae, Nymphaeaceae, and an Austrobaileyales clade (Illiciaceae, Schisandraceae, Trimeniaceae, Austrobaileyaceae). Whereas most recent studies using multiple genes provided poor resolution and support for relationships among the remaining basal angiosperms (Ceratophyllaceae, Chloranthaceae, Canellales (= Winterales), Piperales, monocots, Magnoliales, Laurales), with compartmentalization, we find high levels (> 90%) of bootstrap support for relationships among these clades. Canellales and Piperales form a strongly supported (100%) sister group that is, in turn, sister to a well-supported (100%) clade of Laurales and Magnoliales. Canellales + Piperales and Magnoliales + Laurales form a well-supported magnoliid clade. Ceratophyllaceae are strongly supported (100%) as sister to the monocots; the monocot/Ceratophyllaceac clade is well supported (86%) as sister to all remaining angiosperms (Chloranthaceae, the magnoliid clade, and eudicots). The addition of entire 26S rDNA sequences clearly contributed to this increased internal support. We examined the diversification of perianth phyllotaxis, merosity, and differentiation using our phylogenetic hypothesis for angiosperms. Ancestral perianth phyllotaxis and merosity are equivocal for each node of the Amborellaceac, Nymphaeaceae, Austrobaileyales grade; however, an undifferentiated perianth is reconstructed as the ancestral state for the angiosperms. Trimery and whorled perianth phyllotaxis have played a major role in basal angiosperm perianth evolution and represent the ancestral states for the large clade comprising all angiosperms other than Amborella, Nymphaeaceae, and Austrobaileyales. A differentiated perianth has apparently evolved multiple times.