My primary interests are in the phylogeny, evolution and biogeography of plant groups found on both islands and continents. My research is centered on the large (>1500 species) tribe Vernonieae in the sunflower family, Compositae or Asteraceae. The phylogenetic relationships within the geographically distinctive subtribes, genera and species groups provide ideal systems for tracing the origin and radiation of the tribe and other similarly distributed plant groups across the globe. Members of the tribe are found on all continents except Antarctica and on most island groups around the world. Their geographical distributions also provide opportunities to examine the importance of both long-distance dispersal and vicariance. For example, long-distance dispersal is clearly responsible for bringing the ancestor of Hawaii’s endemic Vernonieae, Hesperomannia, from Madagascar where its closest relative occurs. (There has never been a land connection to the Hawaiian archipelago from any continental area or Pacific island.) Vicariance, on the other hand, may provide the best explanation for the current distribution of taxa in discontinuous habitat types such as dry forests or high elevation volcanoes found throughout the Americas, a question currently under study (see below). Despite being found from Argentina to Canada and in the West Indies in the New World, the tribe originated in eastern Africa /Madagascar and has radiated throughout Africa, to India and southern China as well as to islands in the region. Endemic taxa are also well represented in archipelagos of different sizes and ages. My interests include other groups as well and I look forward to learning more about the biogeography of Pacific and continental species, particularly through projects with my students and post-doctoral associates (see Keeley Lab page).
My current NSF funded research focuses on the relationships of each of two species-rich genera, Critoniopsis and Vernonanthura, in tracing the pathways and timing of the radiations of the tribe in the Americas. Critoniopsis and Vernonanthura are found in South, Central, and North America in montane and lowland habitats, respectively (Fig. 1). The distributions and relationships within and among these genera can provide important information on the effects of major climatic and geological events that have affected the distribution of many plants and animals in the New World. These include the uplift of the Andes, the drying of eastern South America, Pleistocene glaciations and the alternating warm periods with concomitant changes in sea level, the closure of the Isthmus of Panama (the Great American Interchange) and the formation of the modern West Indian islands. Knowing the relationships, habitats and specific locations of both high and low elevation species groups can clarify the availability and timing of major dispersal routes between South and North America during the past 5 MY. The phylogeny of each genus will be reconstructed using DNA sequence data from nuclear and chloroplast genomes. These data will then be used to place the genera within the larger phylogenetic framework of the tribe, e.g., Keeley et al., 2007. Biogeographical analyses will be conducted using DIVA and likelihood methods to explore a range of possible explanations for the patterns observed. These will be correlated with the phylogenetic position of species in both genera and their relative positions within the New World Vernonieae. This big picture approach, as well as that given by the smaller species groups, are significant because together they allow us to understand not only the biogeography of the tribe, but also contribute to our understanding of the patterns of radiation of the family within the New World. The Vernonieae is the only tribe in the Compositae with genera widely radiated in South, Central, and North America in both montane and lowland habitats and is therefore especially well suited to this multi-faceted approach. Additionally, I am working with Nok Bunwong (Khon Kaen University, Thailand) and Harold Robinson (Smithsonian Institution, Washington, D.C.) on the relationships of Thai Vernonieae to those found to the west in India and Africa and those found to the east in China and Malaysia to add to our overall understanding of tribal evolution and global radiations.
This research involves students and faculty from Brazil, Mexico, University of Hawaii at Manoa and colleagues at the Smithsonian Institution, Field Museum and the Fairchild Botanical Garden. Graduate and undergraduate students participate in the research and data analyses. The Vernonieae are particularly well represented in Brazil and a mini-symposium at the University of São Paulo will be held in June 2011, to promote collaboration among students who are actively working in Compositae systematics and who will be taking the lead in Latin America in the future. In addition, we are providing new data and expanding public access to information on the Compositae through the Encyclopedia of Life (C-EOL) and The International Compositae Alliance (TICA).