Oenothera

Tutin, T.G., Heywood, V.H., Burges, N.A., Moore, D.M., Valentine, D.H., Walters, S.M. & Webb, D.A. 1968: Flora Europaea 2
1Hypanthial tube 30-50 mm long; petals 40-60 mm long
1'Hypanthial tube 70-100 mm long; petals 32-40 mm long