William (Bil) Alverson and coauthors at other institutions used rbcL sequences to delimit the "expanded Malvales" and to show that the core four families (Tiliaceae, Sterculiaceae, Bombacaceae, and Malvaceae) form a monophyletic clade (Alverson et al., 1998). Using this as a basis, we have resolved relationships among 70 representatives of the core families using sequences of the chloroplast gene ndhF (Alverson et al., 1999). The consensus of the most-parsimonious trees shows that the core Malvales is divided into two primary clades, the "lower" Malvales which includes most Tiliaceae plus half of Sterculiaceae, and the "upper" Malvales, which includes all traditional Malvaceae and Bombacaceae plus some Tiliaceae (Tilieae, Brownlowieae, and Berryeae) and the rest of traditional Sterculiaceae. The upper Malvales is supported by a distinctive, unreversed 21bp in the ndhF gene.We have proposed a high-level systematization of core Malvales (Baum et al. 1998). All taxa we have named have been provided with phylogenetic definitions. We are continuing our research into phylogeny of the core Malvales with a focus on some particular clades (see below). We are coordinating our research with Mark Chase, Clemens Bayer, and Frank Blattner so as to facilitate a multi-authored combined analysis aimed at resolving remaining points of uncertainty.
Barbara Whitlock (now a Darwin fellow at the University of Massachusetts, Amherst) has been working on the phylogeny of Theobroma, the source of cocoa and chocolate, and its relatives in the clade /Byttneriina (traditionally Sterculiaceae). This work is collaborative with Dr. Clemens Bayer (Palmengarten, Frankfurt). In addition, she has completed and study of the relationships of within the genus Theobroma and its sister genus, Herrania, using a nuclear seed storage protein gene, VICILIN for phylogenetic inference (Whitlock and Baum, 1998).
Reto Nyffeler, is studying the genus Durio and its relatives. This group is interesting because it has traditionally been treated as Bombacaceae, tribe Durioneae, but the molecular phylogeny shows that these Asian trees are more closely related to taxa normally placed in Sterculiaceae than to members of Bombacaceae. The group contains the Durian (Durio zibethinus), which produces a large, spiny fruit with a noxious smell that is (surprisingly!) much sought after for human consumption. A phylogeny of the Durioneae based on ITS and ndhF clarifies the group's evolution and contradicts the famous "Durian theory" of E.J.H. Corner (Nyffeler and Baum, 2000).
We are attempting to resolve relationships in the /Bombacoideae and in the basal lineages of the /Malvoideae using combined analysis of ndhF and matK. We hope to use combined analyses to resolve the group's phylogeny and to locate the acceleration in the rate of molecular evolution seen in the core /Malvoideae. This research effort is being coordinated with John LaDuke (Univ. N. Dakota) and Bernard Pfeil/Curt Brubaker (CSIRO, Canberra, Australia).
We are beginning to characterizing the florally-expressed MADS-box gene family from select /Malvoideae (Hibiscus, Gossypium, and Pavonia) using RT-PCR and genomic PCR. The aims are to characterize the evolution of this gene family in /Malvaceae, to evaluate these genes' utility for phylogenetic inference in the group, to see if expression domains within flowers resemble those known in model genetic systems, and to see if the production of a pigmented calyx and epicalyx in Pavonia strictiflora correlates with "ectopic" expression of B-groups MADS genes. Similar work is being carried out by Randy Small in cotton.Return to Baum homepage