Hybrid origin of the arctic × Pucciphippsia vacillans (Poaceae): evidence from Svalbard plants

The hypothesised hybrid origin of the High Arctic grass × Pucciphippsia vacillans from the putative parents Puccinellia vahliana, Phippsia algida or Phippsia concinna was investigated by analyses of morphological, cytological, and enzymatic data. Chromosome counts showed that × P. vacillans from Svalbard is triploid (2n = 21) and sterile, supporting the hypothesis of a hybrid origin. Enzymatic investigations showed that × P. vacillans is identical to Phippsia in most enzyme markers and furthermore that all four taxa are closely related. Additive banding pattern in one enzyme system (6-PGD) as well as some morphological traits indicated that × P. vacillans is a Puccinellia × Phippsia hybrid. × Pucciphippsia vacillans is morphologically intermediate between Phippsia algida and Puccinellia vahliana in several individual characters as well as in a multivariate analysis, indicating that Phippsia algida is the more probable Phippsia parent. Mature seeds have never been observed in × P. vacillans and the taxon has no known mode of vegetative reproduction. This investigation suggests that it might be a sterile first-generation hybrid wherever it occurs in Svalbard. The close genetic relationship between × Pucciphippsia, Phippsia, and Puccinellia vahliana has implications for their generic delimitation and might suggest that only one genus is involved.