Duthieeae, a new tribe of grasses (Poaceae) identified among the early diverging lineages of subfamily Pooideae: molecular phylogenetics, morphological delineation, cytogenetics and biogeography

The phylogeny of Pooideae, one of the largest subfamilies of grasses, has been intensively studied during the past years. To investigate the early evolutionary splits in Pooideae we used a broad sample of genera with uncertain placement, some of which have not been studied in molecular phylogenetics before, complemented by representatives from other lineages of this subfamily. Morphological, cytogenetic and biogeographical analyses were added to the molecular sequence work on chloroplast matK–3'trnK and nuclear ITS. According to chloroplast DNA data, a new and well-supported lineage was identified among the early branches. It consisted of Phaenosperma and a larger group of genera encompassing Anisopogon, Danthoniastrum, Duthiea, Metcalfia, Pseudodanthonia (inclusion resting on ITS and morphology), Sinochasea and Stephanachne. Based on structural characters we suggest to keep Phaenosperma under the monotypic tribe Phaenospermateae and to accommodate the other genera under a new tribe Duthieeae, which is morphologically well-defined by synapomorphic spikelet features. Megalachne and Podophorus were not part of the early diverging Pooideae lineages but belong to the Aveneae/Poeae complex. Morphological characteristics of Duthieeae are discussed with respect especially to Stipeae and reveal consistent differences between both tribes. The genera of Duthieeae and the major lineages of Stipeae are keyed. A cytogenetic survey of exemplary taxa corroborates high chromosome base numbers as prevailing within the early diverging lineages of Pooideae, but chromosome sizes are more highly varied than previously reported. Ecogeographical analyses point to warm and humid conditions as the ancestral bioclimatic niche of Phaenosperma and Duthieeae, whereas adaptation to cold and drought occurred only in a part of Duthieeae but was obviously less successful than in the widespread and much more species-rich tribe Stipeae. The distribution of Duthieeae with species-poor or monotypic genera in mountains of the northern hemisphere and Anisopogon as an outlier in Australia suggests relict character. Key words: biogeographycytogeneticsDuthieeaegrassesITSmatKmorphology Phaenosperma phylogeneticsPoaceae Acknowledgements We would like to thank Gunter Karste (Harz Mountain National Parc, Wernigerode), Georg and Sabine Miehe (Marburg University), Robert J. Soreng (Smithsonian Institution, Washington, DC), Natalia V. Tkach (Halle), Nikolai N. Tzvelev (Komarov Institute, St. Petersburg), and the herbaria listed in Appendix 1 for supplying plant material to our study. Further we are very grateful to Bärbel Hildebrandt for excellent technical help and to Anne Blaner, Katja Perner and Ina Schneider for carrying out the analysis of some sequences during a practical course. Work was supported by a fellowship from the State of Saxony-Anhalt to JS. Associate Editor: Charlie E. Jarvis Notes aThe incision of the lemma was calculated as proportion of the lateral lobes/awns relative to the entire lemma excluding the median awn. The threshold value for 'yes' is ≥1/3. For Anisopogon we included in the measurements the entire lateral awns, which surmount the scarious lobe adherent at their base. Other works included only the scarious lobes to calculate the depth of the lemma incision and thus mention deviant proportions (e.g. CitationSharp & Simon, 2002; CitationClayton et al., 2006 onwards). bThe lemma of Stipinae is comparatively deeply incised in Celtica gigantea and Macrochloa tenacissima (c. 1/3 of lemma length), but the incision is confined to the narrowed lemma apex as in some species of Achnatherum and Ptilagrostis, whereas the broadened lemma body below is undivided, in contrast to Trikeraia hookeri. Trikeraia hookeri is the seemingly only species of Stipeae with an incision of the lemma reaching into the green body of the lemma as typical of Duthieeae, but it differs by the absence of a rachilla extension from the latter (see text for further explanation). cThis study. dNot examined. eThe minute rachilla extension in this species is not necessarily present in all spikelets of the inflorescence. In case of doubt several florets need to be checked. f Ampelodesmos has a briefly bifid lemma tip with a short awn arising from the sinus, or the awn is absent. g2-keeled only in Lorenzochloa, Piptochaetium and some species of Austrostipa (CitationWatson & Dallwitz, 1992 onwards). hIn Psammochloa (CitationWatson & Dallwitz, 1992 onwards). aAssuming that monoploid chromosome numbers ≥13 are already based on polyploidy (CitationHunziker & Stebbins 1987). bThis count in plants from Bulgaria most likely rests on misidentified plants. An occurrence of Danthoniastrum is not documented for this country to date (CitationWinterfeld, 2006; CitationDöring et al., 2007).