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Biological Sciences

College of Arts & Sciences

Tim McDowell

Tim  McDowell 

Professor Emeritus
Brown Hall, Room 331

Research Interest:

Exostema and the Neotropical Rubiaceae 
I study the taxonomy (scientific naming and classification) and phylogeny (evolutionary relationships) of Exostema and of related groups in the Coffee-Quinine family (Rubiaceae). Exostema is a remarkably diverse genus of 25 species of shrubs and trees which grow in tropical/subtropical regions of the Americas, mostly on the islands of Cuba and Hispaniola. I'm especially interested in the pollination biology of these species (bees, butterflys and moths are involved), their biogeography (migrations from South America to the West Indies over tens of millions of years colonized the islands), speciation (why are so many species in Cuba, the Dominican Republic and Haiti?), and ecological specializations (how did this group evolve from large rainforest trees into spiney desert shrubs and long-flowered river-bed plants?). I use morphological and DNA data to investigate phylogenetic relationships. My taxonomic research involves study of herbarium material (dried pressed plant specimens) and the historical record (literature) for these species. I do field work in the Caribbean region to collect and study the plants and their ecology in the wild. Exostema also included many medicinal plant species, which are effective against the malaria parasite, Plasmodium falciparum , according to modern and historical reports.

Caribbean Biogeography 
Biogeography is the study of plant and animal distributions and the processes that produce these patterns. The Caribbean region includes the islands of the Greater Antilles (Cuba, Hispaniola, Jamaica & Puerto Rico), the Lesser Antilles (the smaller islands from San Marteen to St. Lucia), and surrounding continental regions of North, Central and South America. My studies of Caribbean Biogeography seek to discover and document the various paths taken by the plants of the Caribbean as their ancestors migrated and separated during their evolutionary journey. Comparing the distributions of related species with their evolutionary tree can reveal where a group originated, where it ended up, and how it got there. In the genus Exostema there appear to have been several migrations to the Antilles, including one via the uplands of South and Central America, and one via the lowland forests of Amazonia and the Lesser Antilles. 

Flora of the Southern Appalachians 
East Tennessee is graced with a richly diverse flora. Spring wildflowers abound, a large number of trees and shrubs populate our hardwood and evergreen forests, and various special habitats such as bogs, rock outcrops, mountaintop balds and limestone ridges are host to many rare and unusual plant species. A nearby locality, Roan Mountain, has been a focus of botanical interest for 150 years, and is host to many rare and disjunct species of plants. The spruce-fir forest of Roan Mountain represents one of the most southern sites for this typically northern evergreen forest type, and many northern plant species occur on Roan Mountain as relicts from their the ice ages distributions. 

Selected Publications:

McDowell T. & B. Bremer. 1998. Phylogeny, diversity, and distribution in Exostema (Rubiaceae): implications of morphological and molecular analyses. Pl. Syst. Evol. 212: 215-246. 

McDowell, T. 1996. Syringantha coulteri (Hooker f.), a new combination, and remarks on the relationships of the monotypic genus Syringantha Standley (Rubiaceae), Novon 6. 273-279. 

Levy, F., S. Hill and T. McDowell. 2001. Wind-stress: An experimental investigation into the structure-function relationship of leaf architecture. Amer. Biol. Teacher 63:124-127.


  • Biology for Non-majors I (BIOL1020)
  • Plant Systematics (BIOL 4337/5337)
  • Tropical Botany in Ecuador (BIOL4377/5377)
  • Plant Diversity (Bryophytes, Ferns & Seed Plants) (BIOL 4450)
  • Dendrology (BIOL4957/5957)
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