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

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 κ = 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: