Circumscription of the Malvales and relationships to other Rosidae: evidence from RBCL sequence data

The order Malvales remains poorly circumscribed, despite its seemingly indisputable core constituents: Bombacaceae, Malvaceae, Sterculiaceae, and Tiliaceae. We conducted a two-step parsimony analysis on 125 rbcL sequences to clarify the composition of Malvales, to determine the relationships of some controversial families, and to identify the placement of the Malvales within Rosidae. We sampled taxa that have been previously suggested to be within, or close to, Malvales (83 sequences), plus additional rosids (26 sequences) and nonrosid eudicots (16 sequences) to provide a broader framework for the analysis. The resulting trees strongly support the monophyly of the core malvalean families, listed above. In addition, these data serve to identify a broader group of taxa that are closely associated with the core families. This expanded malvalean clade is composed of four major subclades: (1) the core families (Bombacaceae, Malvaceae, Sterculiaceae, Tiliaceae); (2) Bixaceae, Cochlospermaceae, and Sphaerosepalaceae (Rhopalocarpaceae); (3) Thymelaeaceae sensu lato (s.l.); and (4) Cistaceae, Dipterocarpaceae s.l., Sarcolaenaceae (Chlaenaceae), and Muntingia. In addition, Neurada (Neuradaceae or Rosaceae) falls in the expanded malvalean clade but not clearly within any of the four major subclades. This expanded malvalean clade is sister to either the expanded capparalean clade of Rodman et al. or the sapindalean clade of Gadek et al. Members of Elaeocarpaceae, hypothesized by most authors as a sister group to the four core malvalean families, are shown to not fall close to these taxa. Also excluded as members of, or sister groups to, the expanded malvalean clade were the families Aextoxicaceae, Barbeyaceae, Cannabinaceae, Cecropiaceae, Dichapetalaceae, Elaeagnaceae, Euphorbiaceae s.l., Huaceae, Lecythidaceae, Moraceae s.l., Pandaceae, Plagiopteraceae, Rhamnaceae, Scytopetalaceae, Ulmaceae, and Urticaceae. The order Malvales, as traditionally circumscribed, includes four core families, Bombacaceae (;250 spp.), Malvaceae (1500 spp.), Sterculiaceae (1000 spp.), and Tiliaceae (400 spp.), plus from one to eight other families depending upon author (Takhtajan, 1987, 1997; Cronquist, 1988; Dahlgren, 1989; Thorne, 1992). Considering only the core four families, the order comprises predominantly woody and tropical trees, including several economically important genera such as cotton (Gossypium