YELLOW WATER LILIES (NUPHAR, NYMPHAEACEAE) IN GREAT BRITAIN: A NEW HYBRID, A REAPPRAISAL OF RECORDS, AND A REVISED STATUS OF N. ADVENA

Surveys to clarify the identification of the alien spatterdock (Nuphar advena) in Great Britain (England, Scotland and Wales) showed  that most reported populations included plants that did not have a morphology that agreed with literature accounts of that species.  Some populations had been misidentified, whereas others were morphologically atypical variants of the UK native Nuphar lutea. Many populations included individuals that had a combination of traits characteristic of both Nuphar advena and N. lutea. Visual examination and measurement of two stamen characters (filament and anther length) show that these plants are sterile, and molecular analysis confirms that these populations include a previously undescribed sterile hybrid between Nuphar advena and N.  lutea. Here, we formally describe the hybrid as Nuphar × porphyranthera and provide taxonomic and distribution information on the  parental species for comparison, as well as a key to all known Nuphar taxa in Great Britain. Neither Nuphar advena nor Nuphar ×  porphyranthera show any sign of spreading from sites at which they were almost certainly planted and therefore should not be  considered naturalised in Britain.