Morphological study of the structure and development of longan inflorescence

Abstract

The structure and developmental patterns of inflorescence of longan (Dimocarpus longan Lour.) were studied microscopically and by the naked eye. In inflorescence of longan, compound dichasia are arranged on three to four orders of monopodial axes without the formation of terminal flowers, indicating that longan inflorescence is pleiothyrse; cymose partial inflorescences are arranged on more than two monopodial axes. Most of the monopodial axes had differentiated by the end of November just before the cool season. The first sign of inflorescence formation was the appearance of bract primordia at apical meristems of the preformed monopodial axes, with lateral axes preceding the main axes. Dichasia were formed in the axils of bract primordia, and the formation of bracts and dichasia continued. Bract appearance can be detected by the naked eye 1 week after microscopically detected bract appearance. Shoots with intermediate characteristics between the inflorescence and the vegetative shoots were formed; dichasia were formed on the lateral axes, but not on the main axes in intermediate shoots. These results suggest that apical meristems on the terminal shoot produce monopodial axes, together with foliage leaf primordia, before floral induction, but produce bract primordia and compound dichasia, which are composed of sympodial axes, after floral induction.