My research is focused broadly on mechanisms that generate reproductive diversification in flowering plants. Because mate recognition in plants is a developmental process, I seek to understand the developmental evolution of angiosperm male and female gametophytes and their involvement in the process of double fertilization. Specifically, I have been interested in the evolution of post-pollination mechanisms for mate recognition. My approach has been to study mate recognition in flowering plant groups that lack one or more components of the “typical” angiosperm reproductive syndrome.

In angiosperms, a long chain of reproductive events can mediate fertilization and the reproductive success of the zygote. Mate selection processes can occur at the time of pollen shedding, pollen reception, pollen tube growth, double fertilization, embryo/endosperm growth, seed maturation. A unique feature of flowering plants that promotes mate recognition after pollination is the closed carpel. The closed carpel and associated structures (stigma, style, transmitting tract, inner surface of carpel) causes the potential for positive and negative interactions between pollen tubes and female sporophytic tissues. Its origin is said to have given flowering plants the novel ability to “screen” pollen tubes. But some of the earliest branching lineages of flowering plants lack some or most of the traits associated with the closed carpel, and we know virtually nothing about mate recognition in these taxa. I have initiated a project to study post-pollination processes that mediate differential pollen tube success in early lineages of angiosperms. Specifically, the project aims to understand the developmental and genetic basis of early angiosperm breeding systems.

A second and related project concerns the role of post-pollination processes in mediating genetic and genomic diversity in members of the Fagales complex. These taxa are largely wind-pollinated but outgroup analysis suggests that their ancestors were insect-pollinated. Thus, most Fagales have lost an important pre-pollination mechanism for mate selection (insect pollination and showy flowers), and, in fact many Fagales members are famous for extreme outbreeding (and interspecific hybridization). Ecological divergence has long been thought to explain diversification within this order. But I have shown that various post-pollination processes contribute significantly to maintaining species identities in two families. I have ongoing work in oaks (Quercus) and birches (Betula) of North America.