As a student of Dr. Graves, I recently earned a Master's degree for work in which I evaluated the North American native shrub, eastern leatherwood (Dirca palustris). The primary goals of my projects were to identify natural variation in phenotypic traits across the broad range of the species and to quantify genetic variation across this range. In doing this, we identified a population of Dirca in Florida that contrasts with the accepted description for Dirca palustris in that it has white pubescence on bud scales instead of the brown described for the species (photos below). A short note in which we described this finding was published in the ecology journal, Rhodora.

The most interesting aspect of my Master's experience was traveling from site to site across the Eastern United States to five populations spanning the distribution of eastern leatherwood from Florida to North Dakota. I did this to document variation in floral and vegetative traits, and to collect tissue samples of indigenous plants for evaluation of genetic diversity. In all, I made at least three trips to each site, which ended up being quite a bit of traveling! I am now putting the final touches on a manuscript documenting the extent of variation found across the range of eastern leatherwood. The primary conclusions of this work are that the populations of leatherwood in Florida and North Dakota are phenotypically and genetically distinct among the five populations I assessed, and that the populations more toward the center of its range are relatively similar to each other.

Horticulturally, we are also interested in leatherwood's potential in managed landscapes. Because the species is difficult to grow in the greenhouse, we sought to identify root-zone conditions that promote the growth of eastern leatherwood. We found that the species is sensitive to root-zone pH in horticultural substrates, and that acidic root zones fostered the greatest performance of seedlings. Results of this work were recently published in HortScience.

A project I am still working on seeks to quantify rates of clonal reproduction versus sexual reproduction in the five populations I visited over the past two years. The species is known to spread via rhizomes in the wild, but the extent to which leatherwood relies on clonal spread for population persistence is unknown. This is worth pursuing because such information is valuable from a conservation biology perspective. The extent to which a species is clonal versus sexual has implications for its genetic diversity and the security of populations under conditions of a changing climate.

I decided to remain at Iowa State University with Dr. Graves as my advisor for my PhD work. The kind of work conducted in this lab is important to the fields of horticulture and ecology, as it builds valuable connections between ornamental horticulture, physiological ecology, and population ecology. Such interdisciplinary perspectives are as important as ever, as the more science discovers about the natural world, the more we come to understand that none of the biological sciences (including horticulture) can be practiced independently from ecological considerations or without regard for ecological consequences. Because of this, I am co-major in Ecology and Evolutionary Biology and Horticulture for my doctoral work. It is in this spirit that I am planning my PhD projects, with an interest in the evolutionary development of drought adaptation among closely related woody plants occupying contrasting habitats in North America. Of particular interest to me are genera that occupy both the eastern temperate deciduous forests of North America and the comparatively droughty Mediterranean climate in California.

Inflorescences of Dirca palustris. 1. White pubescence on bud scales of a plant in its native habitat in northwestern Florida. This pubescence color is inconsistent with the existing description of the species. 2. Brown pubescence on bud scales of a plant in its native habitat in southern Illinois. The description of D. palustris includes brown pubescence as a hallmark of the species. For more information, see: Peterson, B.J., Graves, W.R., and J. Sharma. 2009. Color of pubescence on bud scales conflicts with keys for identifying species of Dirca (Thymelaeaceae). Rhodora 111:126-130.

First-year seedlings of eastern leatherwood cultured in the greenhouse. The species is especially slow-growing and seedlings generally produce, at most, several inches of growth per year.

Native habitat of eastern leatherwood at a research site in southern Illinois. The species is largely restricted to stream banks and slopes in shady forest understories. This site, in the Shawnee National Forest, was nestled within dramatic topography, picturesque creeks and streams, and plenty of native plant and animal diversity. Leatherwoods are visible in the right half of the image, in the shadows of a large rock outcrop.

Eastern leatherwood in bloom in Buck's Pocket State Park in northeastern Alabama. The indigenous habitat here is a somewhat steep and rocky forested slope above a large creek - prime habitat for eastern leatherwood! The species flowers and leafs out before trees in the overstory have done so - this may be a way of capturing energy from sunlight early in the season, before the overstory closes in and the leatherwoods become densely shaded.

A photo of me studying the floral display of eastern leatherwood at a research site in Florida. This site represents the southern limit of leatherwood's geographic range.