Nuphar species

Lansdown, Richard & Ruhsam, Markus, 2022, YELLOW WATER LILIES (NUPHAR, NYMPHAEACEAE) IN GREAT BRITAIN: A NEW HYBRID, A REAPPRAISAL OF RECORDS, AND A REVISED STATUS OF N. ADVENA, Edinburgh Journal of Botany 79 (1925), pp. 1-15 : 10-13

Key to Nuphar species in Great Britain

1a. Sepals 6 (usually 3 or occasionally 4 green outer and 3–8 yellow inner) _____________ 2

1b. Sepals 5 (usually 2 green outer and 3 mainly yellow inner) __________________________ 3

2a. Anthers not developing, of uniform colour, reduced to two raised lines at the end of the filament; fruit not produced; leaves typically degrading in July ___ Nuphar × porphyranthera

2b. Anthers dehiscing, pollen yellowish white in two lines, contrasting with the colour of the anther; fruit produced; leaves persisting at least into September ________ N. advena