Data from: Out of Africa to Madagascar - then back? Molecular phylogenetics and biogeography of tribe Tarchonantheae (Asteraceae: Tarchonanthoideae)

Premise of research. Molecular data have revolutionized inferences of
phylogenetic relationships and historical biogeography of flowering
plants. Two small genera, Brachylaena and Tarchonanthus, are the only
members of Asteraceae tribe Tarchonantheae (subfamily Tarchonanthoideae).
The tribe is morphologically distinct within Asteraceae and is resolved as
monophyletic with molecular markers. It is distributed in southern Africa
and Madagascar. The purposes of the present study were to determine
whether molecular data resolve the two genera as monophyletic and to infer
the origin and dispersals that produced the current distribution of the
tribe. Methodology. Sequences from the nuclear ribosomal ITS and ETS and
plastid rpl16 intron were analyzed using maximum likelihood and Bayesian
analyses to resolve phylogenetic relationships within the tribe. An
ancestral trait reconstruction assessed the likely ancestral range for
Tarchonantheae using BioGeoBEARS, and BEAST was used for dating
divergence. Pivotal results. We resolved Tarchonanthus as a monophyletic
group nested within Brachylaena, making the latter genus paraphyletic. All
Malagasy species occurred within a strongly supported clade, but also
resolved within the clade was the widely distributed African species
Brachylaena huillensis. This indicates two dispersal events between Africa
and Madagascar—either a single dispersal to Madagascar, followed by back
dispersal to Africa, or two independent dispersals from Africa. 
Conclusions. Tarchonanthus is a monophyletic group nested within
Brachylaena, rendering the latter genus paraphyletic. An initial dispersal
of Brachylaena from Africa to Madagascar with subsequent speciation,
followed by back dispersal to Africa, with minimal morphological
divergence between the African species and its sister species in
Madagascar could explain the current distribution of Brachylaena.
Alternatively, there may have been two dispersal events to Madagascar from
Africa during the Miocene, but all within the same subclade. Dispersal of
flowering plants back to Africa from Madagascar is very rare, if not
unprecedented. These dispersal events, and most diversification within the
tribe, including the divergence of Tarchonanthus and Brachylaena, took
place during the Miocene.