The diversity of leaf shapes in the natural world drove early naturalists to pose questions about how and why they differ among the many groups of plants on earth. Charles Darwin (1859) described the study of morphology as ".the most interesting department of natural history, and may be said to be its very soul." This project examines the evolution and development of leaves in the fern genus Pleopeltis (in the family Polypodiaceae). As recently reported in the journal Nature and discussed on National Public Radio (April 2004), the Polypodiaceae is a relatively young and very diverse group, second in size only to flowering plants. Even though they evolved very recently, the species in Pleopeltis have a set of leaf shapes nearly as varied as those seen in all plants, living and extinct. How did evolution rapidly generate this diversity of morphology? This research has three components: 1) examining mature leaf forms, 2) examining leaf development, and 3) placing this information in an evolutionary context. NSF funding will support travel to make field collections from natural populations in Ecuador and Mexico, to complement collections already made in Costa Rica. In these three regions, taken together, one can find nearly all of the species in Pleopeltis.
This research will provide important experience and training for a doctoral student, and it will support international collaboration with researchers in Ecuador and Mexico. The resulting comprehensive living collection of Pleopeltis species will make possible numerous research projects that could be undertaken by high school, undergraduate, or graduate researchers. Living plants will also be made available to students as part of the teaching collection. Pressed specimens of field-collected plants will become part of the research and teaching collections in the University of Colorado Museum, as well as at institutions in Ecuador and Mexico. Results of this research will be presented at professional conferences and to the general public through the University of Colorado Museum and the Denver Museum of Nature and Science. Understanding leaf development and evolution is of broad scientific interest, yet has important applications, such as the improvement of crop plants. Studying ferns is essential, since this major group has been understudied compared to flowering plants, even though many fern species are economically important, either as crop plants or as invasive weeds. Ultimately, this research will provide a deeper understanding of the evolution and development of leaf form throughout the plant kingdom.
