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First published online July 20, 2009; doi:10.3732/ajb.0800252 American Journal of Botany 96: 1487-1499 (2009) © 2009 Botanical Society of America, Inc.

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Stem architecture in Eleocharis subgenus Limnochloa (Cyperaceae): Evidence of dynamic morphological evolution in a group of pantropical sedges¹

School of Biological Sciences and Center for Integrated Biotechnology, Washington State University, Pullman, Washington 99164-4236 USA

ABSTRACT

We examined phylogenetic relationships and patterns of stem structural evolution in Eleocharis subgenus Limnochloa, an ecologically and economically important group of tropical to temperate-growing sedges, whose stems serve as the primary photosynthetic organs. We used maximum parsimony, likelihood, and Bayesian inference to develop phylogenetic trees and stochastic mapping and a Markov one-rate model to develop character history reconstructions of stem architecture. A complex history of stem shape evolution characterized by a high degree of homoplasy and rapid rates of change (an average of 13 transitions per character history for about 25 species) was identified across subgenus Limnochloa. Character states transition much more frequently in some lineages than others, but tend to follow a consistent directional pattern of evolutionary change. Our data also suggest that changes in stem shape and anatomy may be associated with speciation events in the subgenus (Pagel’s = 0.3503, P = 0.04579) and may have some adaptive significance. The potential adaptive roles of stem structural traits are unclear, but may be elucidated by further studies. This work serves as a starting point for future evolutionary studies of stem shape and structure in monocots and provides important background knowledge for further studies of ecological adaptations of Eleocharis.

Key Words: Bayesian inference • character evolution • Eleocharis subgenus Limnochloa • geiger • phylogenetics • stem structural evolution • stochastic mapping

Received for publication 22 July 2008. Accepted for publication 18 March 2009.

FOOTNOTES

¹ The authors thank W. Warrington for invaluable field support; L. Harmon and C. Brock for guidance and assistance with geiger; the Northern Territory Government, D. Dixon, I. D. Cowie, B. Harwood, and L. Stanberg for help in Australia; DGB Bolivia, S. G. Beck, A. Lliully A., and R. Isela M. for making Bolivian collections possible, K. M. Redden, K. J. Wurdack, P. Benjamin, C. Perry, D. Singh, E. Liverpool, and the village of Isseneru for so much support and friendship in Guyana; and M. King, J. R. Clark, S. J. Jacobs, and J. P. Riser for support and friendship at home. Thanks as well to F. Bowcutt and J. Longino of Evergreen State College for cultivating the seed of science in a young botanist’s mind. This work has been supported by NSF grant 0515975 to E.H.R.

² Author for correspondence (plantboy{at}gmail.com)

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