Hybridisation and introgression in British Helosciadium (Apiaceae).

Reticulation between Helosciadium repens (Jacq.) W.D.J. Koch and H. nodiflorum (L.) W.D.J. Koch (Apiaceae) has been the source of much speculation, but until now supporting evidence has remained largely anecdotal. In the current study inter-specific hybridisation and introgression between the two species was confirmed using DNA barcoding. The parentage of three putative hybrids collected from Port Meadow, Oxfordshire (UK) was determined using a maternally-inherited chloroplast marker (rps16-trnK) and two biparentally-inherited nuclear markers (LEAFYi2, ITS). Two of the individuals are early-generation hybrids between H. repens and H. nodiflorum, F1 or otherwise, while the third is most likely a backcross to H. repens. These individuals are the first confirmed hybrids/hybrid derivatives between the two parental species, and represent a new addition to the British flora. The hybrids closely resemble H. nodiflorum var. longipedunculatum F.W. Schultz, and in our view should be treated as H. × longipedunculatum (F.W. Schultz) Desjardins.