Rare hybrid swarm of Pilosella polymastix × P. officinarum: cytotype structure and modes of reproduction.

We studied a small, spatially limited population of Pilosella plants, rich in morphological types, in the southwestern part of central Bohemia, Czech Republic. The following tetraploid parental Pilosella species putatively gave rise to the hybrid swarm analysed: sexual P. officinarum and apomictic P. polymastix (P. bauhini–P. caespitosa). In addition, the swarm consisted of (i) a stabilized tetraploid apomictic P. melinomelas (P. officinarum<P. polymastix) represented by two isozyme phenotypes (one dominating), and (ii) tetraploid and sexual hybrids between P. officinarum≥P. polymastix, with 16 isozyme phenotypes in the 18 plants analysed. We also found pentaploid P. bauhini (three plants comprising one isozyme phenotype), one hexaploid plant corresponding to P. melinomelas (putative 2n + n hybrid) and one pentaploid plant (probably a hybrid between hexaploid and unknown tetraploid). The single triploid plant detected in the hybrid swarm is probably of polyhaploid origin. Both P. polymastix and P. melinomelas are rare hybrid species, which because they had not been recorded for many years were considered as probably extinct in the Czech Republic.