Abstract: Floral nectaries attract insect pollinators through secreted nectar. The structure and the size of floral nectaries are determining factors of the quantity and concentration of the nectar produced, which may consequently influence the patterns of insect visitation. In this study, we examined the structural and developmental characteristics of the floral nectaries of Litchi chinensis of "Nuomici" and "Feizixiao". In two variety of L. chinensis, the floral nectaries of both functional male and female flowers are located between the cup-shaped calyx and the ovary. These floral nectaries are typical structural nectaries, formed as protrusions on the surface of flower receptacles, and at the mature stage, they are composed of epidermis, nectariferous tissue, and vascular tissue containing only phloem elements. The epidermis of the floral nectaries is covered with numerous epidermal hairs, with sporadic stomata distributed on the top surface of the nectaries. Before the nectaries start to secret nectar, the nectariferous tissues are filled with numerous starch grains, which display regular changes before, during, and after nectar secretion. The nectariferous tissue contains two cell types of different morphological characteristics. These cell types presumably have different functions, either for nectar synthesis, or for protecting nectaries from damage by phenolic compounds. The primordia of these nectaries initiate during floral organ differentiation, and its development coincides with the formation of microspores and macrospores in the male and female flowers, respectively. Based on these structural and developmental characteristics, we discussed the ontogeny and phylogeny of the floral nectaries in L. chinensis and possible evolutional adaptation of nectaries for effective attraction of insect pollinators.

Key words: Litchi chinensis, floral Nectary, morphology development, pollination