Morphological observations on capitulum initiation and floret development of garland chrysanthemum (Chrysanthemum coronarium L)

Morphological properties of capitulum initiaton and floret development of garland chrysanthemum (Chrysanthemum coronarium L.) were observed with a scanning electron microscope (SEM). Sixteen cultivars varying in flowering time were used. The flowering process was classified into 10 stages. A capitulum was initiated from stage 2 (early involucre forming-stage). The differentiation between ray and disc florets occurred at stage 5 (late floret forming-stage). Disc florets has a pistil and five stamens. Disc florets covered the entire surface of receptacle except for one or two layers of ray floret which are located on the periphery of the receptacle between the disc florets and the involucres. A ray florets has a pistil, but no stamen. There were cultivar differences in capitulum size, numbers of ray and disc florets, and involucres. The diameter of the capitulum ranged from 71.0+/-0.0 mm to 42.0+/-6.2 mm; the number of ray florets per capitulum ranged from to 23.7+/-5.4 to 14.2+/-0.5; where the range of disc florets was from to 478.0+/-0.0 to 276.2+/-44.8. The number of bracts (involucres) per capitulum ranged from 41.0+/-0.0 to 27.50+/-5.0. Individual cultivars differed in flowering response between spring and autumn. In the spring, budding in all cultivars occurred earlier than that in autumn. Capitulum of 'Kairyo chuba satoyutaka', 'Tatsunami', and 'Otafuku-A' became visible 10, 15, and 35 days after planting, respectively. In autumn, however, capitulum initation of 'Kairyo chuba satoyutaka' occurred 70 days after planting. The number of nodes from the cotyledon to capitulum in the spring was significantly fewer than that formed in the autumn. The node number of 'Kairyo chuba satoyutaka' was 32.8 in the spring, and 54.7 in the autumn.