Morphology of Capitulum Initiation and Floret Development of Dendranthema Species Native to Japan

Abstract

Capitulum initiation and floret development of seven Dendranthema species (D. boreale, D. indicum, D. japonicum, D. occidentali-japonense var. ashizuriense, D. ornatum, D. pacificum and D. yoshinaganthum) were investigated by scanning electron microscope (SEM). The sequence of events in these seven species was similar. Nine developmental stages were identified : vegetative stage, doming stage, earyly and late stages of involucre and floret formations and early, mid- and late stages of corolla formation. The time of capitulum initiation, its developmental rate and the time of anthesis differed, depending on species. Two types of disc floret development, i.e. petal closed before or after stamen primordia initiation, were observed.