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.
Courses:
- 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)