Puccinellia lineage

Röser, Julia Schneider Grit Winterfeld Martin, 2012, Polyphyly of the grass tribe Hainardieae (Poaceae: Pooideae): identification of its different lineages based on molecular phylogenetics, including morphological and cytogenetic characteristics, Organisms Diversity & Evolution (New York, N. Y.) 12 (2), pp. 113-132 : 129

Puccinellia lineage ( lineage V)

This lineage comprises taxa that were regarded as members of the separate subtribes Puccinelliinae ( Catabrosa , Puccinellia , Phippsia ) and Miliinae ( Colpodium , Zingeria ; cf. Tzvelev 1976; Soreng et al. 2003; 2007; Gillespie et al. 2010). Zingeria and Colpodium are supported strongly as sister taxa by cpDNA data, sharing a deletion of 9 bp in the mat K gene region (Fig. 1; Schneider et al. 2009), and nuclear ITS sequences ( Fig. 2 ; Quintanar et al. 2007; Gillespie et al. 2008; Schneider et al. 2009). They are related also in chromosomal aspects, as the Colpodium versicolor or a closely related genome (x 0 2; Fig. 6g ) was involved in the polyploid evolution of Zingeria ( Kotseruba et al. 2010; cf. Kotseruba et al. 2003, 2005; Kim et al. 2009). Both genera are nested within the lineage V together with Catabrosa , Phippsia and Puccinellia , but in the ITS tree without support (Figs. 1 and 2). This result concurs with previous studies, in which Catabrosa , Phippsia and Puccinellia were placed in a common lineage with either Zingeria or with Zingeria and Colpodium ( Döring et al. 2007; Döring 2009; Schneider et al. 2009) according to cpDNA data. Nuclear ITS data were less decisive and showed larger polytomies or branches without BS, which encompassed members of the Poa lineage ( lineage IV in this study) and included Milium , not sampled in this study ( Quintanar et al. 2007; Gillespie et al. 2008; Schneider et al. 2009). A similar structure was obtained from a combined ITS and ETS data matrix ( Gillespie et al. 2010). According to cpDNA data, however, Milium is nested firmly in the Poa lineage ( Döring et al. 2007; Quintanar et al. 2007; Gillespie et al. 2008; Schneider et al. 2009). Considering classification, this suggests that subtribe Miliinae should be abandoned, and Colpodium and Zingeria acknowledged as members of the Puccinellia lineage .

Cytogenetic analysis

The monoploid chromosome number of x 0 7 and ‘large’ chromosomes prevail within the Aveneae / Poeae tribe complex and the Triticeae incl. Bromeae , but there are exceptions. A previous study corroborated the tendency for a reduction in monoploid chromosome numbers from the early (tribes Brachyelytreae, Stipeae, Nardeae, Meliceae, Phaenospermateae, Duthieeae, Diarrheneae , Brachypodieae) to the late diverging lineages of the subfamily Pooideae (tribe Triticeae , Aveneae / Poeae tribe complex; cf. Schneider et al. 2011). With a broader sampling of genera from the Aveneae / Poeae , the present study shows that chromosome numbers vary in different lineages (I–V; Fig. 1) of this tribe complex between x 0 2 and x 0 13, with even x 0 19 reported in the literature ( Table 4; Fig. 1). The most frequent number is x 0 7, long recognised as characteristic of this group ( Stebbins 1956, 1985; Clayton and Renvoize 1986; Hunziker and Stebbins 1987; Watson and Dallwitz 1992; 1992 onwards; Hilu 2004; Rodionov et al. 2007). Metaphase chromosomes are typically large and more than 4 μm long ( Fig. 6 ).

Chromosome numbers may be variable even within smaller phylogenetic groupings, as seen in lineage I, which usually has chromosome numbers of x 0 7 (Fig. 1), x 0 13 in Hainardia ( Table 4, Figs. 1 and 6c), and different numbers of x 0 7, 9, 19 reported within the genus Parapholis . Scribneria in lineage III also has the uncommon chromosome number of x 0 13. Interestingly, this uncommon chromosome number is well-documented also for its evidenced neighbour genus Deschampsia and is known to occur in D. cespitosa (Figs. 1 and 6a). In Deschampsia , this monoploid chromosome number was probably derived from a dysploid chromosome number reduction in a tetraploid from 2 n 0 28 to 2 n 0 26 and not from hybridisation between parental taxa with monoploid chromosome sets of x 0 7 and x 0 6 and subsequent genome doubling ( Garcia-Suárez et al. 1997; Winterfeld 2006; Winterfeld and Röser 2007). The origin of the monoploid chromosome number of x 0 13 in Hainardia , which has much larger chromosomes ( Fig. 6c ) than in Deschampsia , and of x 0 19 reported in Parapholis , has not yet been investigated. However, it seems likely that these high numbers are actually resting already on polyploidy as in Deschampsia .

Figures

Fig. 2 Bayesian phylogenetic tree obtained from nuclear ITS DNA sequences. Branches collapsed in the strict consensus tree based on maximum parsimony analysis are in bold. Posterior probabilities ≥0.95

Fig. 6 a–g Mitotic metaphase chromosomes. of a Deschampsia cespitosa (2n = 26). b Festuca gigantea 2n=42. c Hainardia cylindrica 2n=26. d Phleum phleoides (2n=14+ 2B). e Vulpia bromoides (2n= 14). f Koeleria cristata (2n= 56). g Colpodium versicolor (2n=4)