Research Interests:

Our research spans a wide range of topics in plant systematics and evolution, involving undergraduate and graduate students as well as international collaborations. Our general research goal is to test systematic and evolutionary hypotheses in a phylogenetic context. We integrate information from DNA sequences, morphology, and fossils to reconstruct the phylogeny of plants and use the phylogeny as a basis to elucidate the biogeographic history (e.g., time and place of origin, time and routes of migration) and to understand the rate and pattern of molecular and morphological evolution, as well as their relationships. We have also expanded our research to study the evolutionary history and mechanisms in plant hybrid zones. The dogwood group (Cornales) has been our main focus. Below is a little more detail about the dogwoods and what we do for plant molecular systematic research.

The dogwood genus Cornus, which includes the big-bracted dogwoods (including our state flower, Cornus florida L.), the cornelian cherries, the bunchberries (or the dwarf dogwoods), and the red osier dogwoods. All are commonly grown as ornamental plants.

Cornus florida –state flower                      Bunchberry                      Cornelian Cherry

   Red Osier Dogwood

 These species are quite different in their clustering of flowers (see pictures). There are about 55 species of dogwoods in the world and most of them are found in eastern North America and eastern Asia. There are a few species in Europe, western North America, one in Africa and one in South America. We study how these plants from different parts of the world are related to each other, where and when the dogwoods first appeared in the world, and how and when they spread to the different continents. To do this, we compare differences in DNA sequences among the species, using information from fossils and morphology to develop and answer these questions.

We also conduct research in collaboration with botanists in England to understand the genetic basis of the flowering forms of the dogwood species. For example, we would like to know what genetic changes occurred in the past that may have brought about the showy large bracts in our state flower and what made the other species stop developing these showy bracts (like the cornelian cherries). Is there any association between the evolutionary changes in floral organ identity genes and floral types?

We also go out in the field and travel to different places to search if there are new dogwood species that are not known to the world. In 2002, Dr. Xiang discovered a new species in southwestern China on a tropical mountain. She named the species after a late American dogwoods expert, Dr. Richard Eyde, who was a botanist in the Smithsonian Institution at Washington DC. The new species was named Cornus eydeana (see picture). It is an evergreen species producing more flowers and larger fruits, different from all known species of cornelian cherries.

Cornus eydeana

We also conduct research on other plants including the buckeye genus (Aesculus) and the federally endangered species, the smooth coneflower (Echinacea laevigata). Aesculus is group of plants that are highly cultivated for their showy inflorescences and dense green foliage. Three closely related southeastern US species of the genus hybridize frequently and form a hybrid zone in northern Georgia and adjacent area. We conduct molecular genetic analyses to determine the underlying mechanisms involved in the formation and maintaining the hybrid zone. Specifically we would like to know if local or long distance gene flow between species or both have resulted in the hybrid zone, and what is the relative contribution of seed dispersal vs pollen dispersal. Is the evolutionary dynamics in the hybrid zone similar to that in the parental species? These studies will also help to predict the evolutionary consequences of natural hybridization in Aesculus (e.g., whether new species may be formed).

Aesculus sylvatica                      Echinacea laevigata

The smooth coneflower Echinacea laevigata occurs only in a few states of the SE United States with less than 30 populations. We are conducting a genetic analysis of all populations to see how much genetic variation is present within each population and how much genetic difference exists between populations. We also would like to determine the mating system of the species, e.g., the relative frequencies of outcrossing (due to pollination between flowers from different plants) vs. selfing (due to pollination within the same flower or between flowers of the same plant).

We have graduate and undergraduate students participating in all of these studies (See the link Labs). In the field, we collect small pieces of leaf material and dry it. We also use plant presses to press the sample of the plant, binoculars to find and identify the tree species we are looking for, and cameras with close-up lenses to take detailed pictures of plants. We sometimes also collect seeds from the field to grow them in the greenhouse in the study of the smooth coneflower. In the laboratory, we use mortar and pestles to grind the leaf tissue in a buffer to isolate the DNA from the leaf cells. We then visualize the DNA samples by electrophoresing the DNA samples in an agarose gel stained with ethidium bromide. Purified DNA samples can then be used for subsequent molecular techniques including PCR and DNA sequencing.

We believe that our research work is very exciting. Our research contributes to the understanding of plant biodiversity and the underlying mechanisms and processes that generated the biodiversity we observe today. This knowledge not only helps us to know our world better, but also is important to human welfare in a perspective of conservation and uses of natural resources.

On-Going Research Projects:

Phylogenetic and biogeographic studies of the Dogwood genus Cornus; an integration of morphology, molecules, and fossils -- supported by NSF (2 yrs).

Documenting introgressive hybridization and polyploid speciation in the dwarf dogwood species complex – supported by NCSU FR-D grant (1 yr).

Phylogenetic study of Cornales – Combining chloroplast and nuclear DNA sequence data.

Phylogeography of the flowering dogwood Cornus florida, and the dwarf dogwoods species complex.

Evolution and phylogenetic utility of floral development genes in the dogwood genus Cornus.

Genomic and phenetic consequence of introgressive hybridization and polyploidization in the dwarf dogwoods species complex.

Determining the underlying mechanism and evolutionary consequence of natural hybridization in a broad hybrid zone of the buckeye genus Aesculus.

Current and Pending Grants:

National Science Foundation, Phylogenetic and biogeographic study of the dogwood genus Cornus L. (Cornaceae) (current: 2002-2006).

National Science Foundation, Phylogenetic and biogeographic study of Cornales – integrating molecules, morphology, and fossils (current: 2005-2007).

ISGA: Genome-wide responses to protein misfolding (pending).

Publications