Phylogeny of the core Malvales: Evidence from ndhF sequence data

The monophyly of the group comprising the core malvalean families, Bombacac eae, Malvaceae, Sterculiaceae, and Tiliaceae, was recently confirmed by mol ecular studies, but the internal structure of this clade is poorly understo od. In this study, we examined sequences of the chloroplast ndhF gene (alig ned length 2226 bp) from 70 exemplars representing 35 of the 39 putative tr ibes of core Malvales. The monophyly of one traditional family, the Malvace ae, was supported in the trees resulting from these data, but the other thr ee families, as traditionally circumscribed, are nonmonophyletic. In additi on, the following relationships were well supported: (I) a clade, /Malvathe ca, consisting of traditional Malvaceae and Bombacaceae (except some member s of tribe Durioneae), plus Fremontodendron and Chiranthodendron, which are usually treated as Sterculiaceae; (2) a clade, /Malvadendrina, supported b y a unique 21-bp (base pair) deletion and consisting of /Malvatheca, plus f ive additional subclades, including representatives of Sterculiaceae and Ti liaceae, and Durionieae; (3) a clade. /Byttneriina, with genera traditional ly assigned to several tribes of Tiliaceae, plus exemplars of tribes Byttne rieae, Hermannieae, and Lasiopetaleae of Sterculiaceae. The most striking d epartures from traditional classifications are the following: Durio and rel atives appear to be more closely related to Helicteres and Reevesia (Stercu liaceae) than to Bombacaceae: several genera traditionally considered as Bo mbacaceae (Camptostemon, Matisia, Phragmotheca, and Quararibea) or Sterculi aceae (Chiranthodendron and Fremontodendron) appear as sister Lineages to t he traditional Malvaceae: the traditional tribe Helictereae (Sterculiaceae) is polyphyletic; and Sterculiaceae and Tiliaceae, as traditionally circums cribed, represent polyphyletic groups that cannot sensibly be maintained wi th their traditional limits for purposes of classification. We discuss morp hological characters and conclude that there has been extensive homoplasy i n characters previously used to delineate major taxonomic groups in core Ma lvales. The topologies here also suggest that /Malvatheca do not have as a synapormophy monothecate anthers, as has been previously supposed but, inst ead, may be united by dithecate, transversely septate (polysporangiate) ant hers, as found in basal members of both /Bombacoideae and /Malvoideae. Thus , "monothecate" anthers may have been derived at least twice, independently , within the /Bombacoideae (core Bombacaceae) and /Malvoideae (traditional Malvaceae).