Comparative study of leaf architecture and cuticles of Nelumbo changchangensis from the Eocene of Hainan Island, China, and the two extant species of Nelumbo (Nelumbonaceae)

摘要

Fossil leaves of Nelumbo changchangensis, collected from the Eocene of Hainan Island, China, were studied and compared with those of the extant species of Nelumbo, N. nucifera Gaertn. and N. lutea Willd. The fossil leaves have all the specialized features of extant Nelumbo in leaf architecture, except that the organization of the areolae looks much more irregular than that of extant Nelumbo. Comparisons of the cuticle and epicuticular ultrastructure indicate that: (1) N. changchangensis resembles N. nucifera in that anticlinal cell walls of the lower epidermis are straight along the major veins and near leaf bases and are shallowly undulate with U- to V-shaped undulations inside the areolae; (2) N. changchangensis differs from N. lutea in that anticlinal cell walls of the lower epidermis of the latter are deeply undulate with U-, V- to reversed Omega-shaped undulations inside the areolae; and (3) epicuticular wax crystals are more densely distributed on the leaves of N. changchangensis and N. nucifera than they are in N. lutea. These findings shed significant light on the cuticle differentiation of fossil and extant Nelumbo species. The morphometric comparisons indicate that almost all the synapomorphies of extant Nelumbo were already present by the Eocene, 2015, 180, 123-137.