The monophyly of the group comprising the core malvalean families - Bombacaceae, Malvaceae, Sterculiaceae, and Tiliaceae - was recently confirmed by molecular studies employing rbcL sequence data. The internal structure of this clade is poorly understood, however, limiting our understanding of the evolution of this large group and thwarting any reliable taxonomic classification. In this study, we examined sequences of the chloroplast ndhF gene (aligned length 2252 bp) from 70 exemplars representing 34 of the 40 putative tribes or subfamilies of core malvalean families. The monophyly of one family, the Malvaceae, was strongly supported but the other three families, as traditionally circumscribed, were non-monophyletic. The phylogenetic trees resulting from these analyses indicate the following four major clades: 1) A clade consisting of the Malvaceae plus all traditional Bombacaceae (except some members of tribe Durioneae), plus Fremontodendron and Chiranthodendron, which are usually treated as Sterculiaceae; 2) a strong clade supported by a unique 21 bp deletion and consisting of the aforemention plus some representatives of Sterculiaceae and Tiliaceae, plus Durio and Neesia (both Durioneae); 3) a clade containing genera traditionally assigned to tribes Byttnerieae, Hermannieae, and Lasiopetaleae of Sterculiaceae; and 4) a clade with genera traditionally assigned to several tribes of Tiliaceae. The most striking departures from traditional classifications are that Durio and relatives appear to be more closely related to Helicteres and Reevesia ("Sterculiaceae") than to "Bombacaceae"; that several genera traditionally considered as Bombacaceae (Camptostemon, Matisia, and Quararibea) or Sterculiaceae (Chiranthodendron and Fremontodendron) appear as sister lineages to the core Malvaceae clade; and that Sterculiaceae and Tiliaceae, as traditionally circumscribed, represent polyphyletic groups that cannot sensibly be maintained for purposes of classification. We also discuss supporting morphological characters and recommendations for provisional nomenclature for core Malvales.

Key words: Malvales, ndhF, phylogeny