Delimitation of the genus Schizachyrium (Poaceae, Andropogoneae) based on molecular and morphological data

Abstract

Schizachyrium (Poaceae, Andropogoneae) includes about 60 species distributed in tropical and subtropical regions of the world. In all recent molecular phylogenies of Andropogoneae, representatives of Schizachyrium appear closely related to Andropogon species. The objective of this study was to contribute to the delimitation of Schizachyrium. We performed a phylogenetic study including 38 taxa (>63%) of Schizachyrium, along with representatives of related genera, mainly of Andropogon, yielding a total of 49 taxa. This is the first phylogenetic analysis to include the type species of Schizachyrium, S. condensatum. DNA sequences of two plastid markers (ndhF and trnL-F) were analyzed under Bayesian methods. The results indicate that Schizachyrium is not monophyletic: 26 of the 38 Schizachyrium taxa analyzed are placed in a Schizachyrium s.s. clade that includes the type species of the genus, while 10 taxa are related to Andropogon species and two other species, S. delavayi (from China and India) and S. jeffreysii (from Africa), appear clearly separated. Additionally, 58 morphological characters (41 qualitative and 17 quantitative) were scored for the same 49 taxa and analyzed under the parsimony criterion. Character optimizations showed that (i) the reduced pedicellate spikelets, (ii) with lower glume less than or equal to 0.5 mm wide, (iii) awned, and (iv) without lemma and palea support the Schizachyrium s.s. clade. We propose these four characters as diagnostic features for the delimitation of Schizachyrium s.s.