Dubois A, Remay A, Raymond O, Balzergue S, Chauvet A, Maene M, et al. (2011) Genomic Approach to Study Floral Development Genes in Rosa sp. PLoS ONE 6(12): e28455. Sections of floral meristem and young flower buds (Figure 1A, g–k) were used to define the floral organogenesis steps in R. chinensis cv. Old Blush. Five morphologically distinct developmental stages were easily distinguished under a dissecting microscope. At flower development stage 1, the floral bud is surrounded by bracts, the floral meristem is flat and five sepal primordia are visible. Floral organs subsequently form following a radial gradient so that the most external organs are the more differentiated. At stage 2, petal primordia are apparent on the flank of the hypanthium. At development stage 3 stamens primordia appear on the flank of the hypanthium while petal primordia continue developing. At stage 4, carpel primordia are the last organs that appear in the center of the hypanthium, while the other organs continue developing. At stage 5, all floral organs are apparent, and the hypanthium starts to sink below the perianth and stamens. During the onward development stages the hypanthium continues to form and the flower becomes clearly visible (Figure 1 B). The four types of floral organs continue developing and flowers start opening (VP stage for visible petals) (Figure 1 B). Then the flower fully opens (OF stage for open flower), and finally senesces (SF stage for senescing flowers).
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