Molecular evidence for the hybrid origin of Potamogeton ×subrufus Hagstr. (Potamogetonaceae)

Potamogeton ×subrufus Hagstr. was described as a hybrid between P. lucens L. and P. nodosus Poir.; however, the taxon had not been widely accepted and regarded as conspecific with P. ×fluitans Roth, the hybrid between P. lucens and P. natans L. The origin of P. ×subrufus had been obscured till 2010, when, based on morpho-anatomical treatment, it was shown that P. ×subrufus displays several characters consistently different from those of P. ×fluitans. Here we report a successful amplification and sequencing of nuclear ribosomal ITS1 region from a 115 year-old herbarium specimen of P. ×subrufus, collected in locus classicus by J. Baagöe and preserved in the Herbarium of the Institute of Botany, Jagiellonian University (KRA). Based on the additive polymorphism pattern expressed in the ITS1 sequences of P. ×subrufus, we demonstrate that one of the parents of this hybrid was P. nodosus, as was claimed by Hagström.