MOLECULAR PHYLOGENETICS OF THE MAGNOLIIDAE - CLADISTIC ANALYSES OF NUCLEOTIDE-SEQUENCES OF THE PLASTID GENE RBCL

Nucleotide sequences of the plastid protein-coding gene rbcL from 64 species of 36 families in subclass Magnoliidae sensu Cronquist and representatives of all other major seed plant groups were analyzed by parsimony in a series of four analyses. Ceratophyllum (Ceratophyllaceae) was found to be sister to all other angiosperms. Other magnoliids formed five major groups, roughly corresponding to the Magnoliales, Laurales, Aristolochiaceae/Piperales, Nymphaeales, and Ranunculales/Papaverales. Four magnoliid lineages, those with monosulcate or monosulcate-derived pollen (Magnoliales, Laurales, Aristolochiales/Piperales, and Nymphaeales), and the monocots (with the same type of pollen) formed a weakly supported monophyletic group. The Illiciales (Illiciaceae and Schisandraceae), with a unique type of tricolpate pollen, also fell into this monosulcate clade. Relationships among these major lineages were resolved in all trees, but with low levels of support. Magnoliidae with tricolpate and tricolpate-derived pollen, Ranunculales/Papaverales and Nelumbonaceae, fell into the other large clade of angiosperms, which have sometimes been termed the eudicots. Monophyly of this large tricolpate clade was strongly supported. These results demonstrated a high degree of congruence with the major groups identified in other studies, but they differed in the general relationships of these groups, particularly the monophyly of the monosulcate taxa and the sister-group relationship of angiosperms with the two general pollen types. They also deviated in the specific taxon composition of some major clades.