Populations of Pilosella species in ruderal habitats in the city of Prague: consequences of the spread of P. aurantiaca and P. rothiana

Consequences of Pilosella aurantiaca and P. rothiana (stabilized hybridogenous species P. echioides > P. officinarum) spreading into three semi-ruderal localities in the city of Prague were studied. Numbers of chromosomes / DNA ploidy level and mode of reproduction are given for all the species and hybrids studied. Both P. aurantiaca and P. rothiana are apomictic and tetraploid with 2n = 4x = 36. Pilosella rothiana hybridizes with pentaploid P. piloselloides (P. ×heterodoxa, 2n = 6x = 53/54) and tetraploid P. officinarum (P. ×bifurca, 2n = 6x = 54). Pilosella aurantiaca hybridizes with tetraploid P. caespitosa (P. ×fuscoatra, 2n = 4x = 36), P. piloselloides (P. ×derubella, 2n = 5x = 45), P. officinarum (P. ×rubra, 2n = 6x), P. rothiana (2n = 6x = 54), P. ×bifurca (with 2n = 5x = 45) and P. visianii (tetraploid, 2n = 4x = 36). Hybrids of P. aurantiaca with tetraploid P. ×leptophyton were of two types, the tetraploid hybrid originating from parental reduced gametes and the hexaploid hybrid originating from a reduced and an unreduced parental gamete, respectively. Introgression from apomictic P. bauhini towards sexual P. officinarum was found in a hybrid swarm in one of the populations studied. Evolutionary potential of recent hybrids was evaluated with respect to their mode of reproduction; most of the recent hybrids were not apomictic. It seems impossible to predict the mode of reproduction from that of the parental species.