BAUM, DAVID A.1*, ALAN YEN2, BARBARA A. WHITLOCK3, WILLIAM S. ALVERSON4, RETO NYFFELER5, STACEY SMITH1, and REBECCA OLDHAM1. 1Botany Department, University of Wisconsin, Madison WI 53706; 2LifeSpan Biosciences, Seattle WA 98121; 3Organismic & Evolutionary Biology, University of Massachusetts, Amherst MA 01003; 4Environmental & Conservation Programs, The Field Museum, Chicago IL 60605; 5Institut für Systematische Botanik, Zürich, Switzerland. - Mode, locus, and tempo of evolution in Malvoideae and Bombacoideae (Malvaceae s.l.): Evidence from multiple DNA sequences.
Recent molecular phylogenetic analyses have shown that the traditional
mallow family, Malvaceae s.s , is nested within Malvoideae, the most
speciose of the nine major clades in the expanded Malvaceae. These
studies have indicated that Malvoideae is sister to Bombacoideae
forming together the clade Malvatheca diagnosed by highly modified
anthers. In this study we conducted a combined analysis of
trnK/matK (ca. 2.6 kb) and ndhF (ca. 1.8 kb) from 35
representatives of Malvatheca and 22 outgroups. These data do not
provide a definitive placement of Fremontodendreae, Septotheca,
Patinoa, and Ochroma relative to Bombacoideae and
Malvoideae. The core Bombacoideae (= Bombax s.l., Ceiba
s.l., Cavanillesia, and Adansonia) is well-supported but
poorly resolved internally due to insufficient molecular variation.
The inclusion of Matisieae within Malvoideae, sister to
Pentaplaris + core Malvoideae, is well-supported. This topology
is consistent with monothecate anthers of core Malvoideae and core
Bombacoideae representing independent derivations from polysporangiate
(septate) anthers as found, for example, in Ochroma,
Septotheca, and Phragmotheca. The base of core
Malvoideae is unresolved among the Neotropical Uladendron and
several Australasian/Pacific taxa (Camptostemon,
Lagunaria, Radyera, Howittia). Combined with the
ancestrally Neotropical distribution of all other lineages of
Malvatheca (including Matisieae and Pentaplaris) the most
parsimonious model is for a single major dispersal from South America
into the Pacific basin. Fossil data suggest that this dispersal
probably happened in the late Paleocene to early Eocene. Then, after a
period of radiation in the Pacific, two major, radiations occurred,
the Gossypieae + Malveae and the redefined Hibisceae (including
Malvavisceae). It is noteworthy that the rate of molecular evolution
is greatly accelerated in the core Malvoideae relative to its
Neotropical ancestors. However, it may be that the increased rate of
molecular evolution predates the major bursts of speciation, which are
concentrated in Gossypieae+Malveae and Hibisceae.
Key words: biogeography, Bombacoideae, Malvaceae, Malvoideae, molecular evolution