Abstract

Information from phylogenetic trees implies zygomorphic flowers have evolved independently from their actinomorphic ancestors several times. There are various types of zygomorphic flowers in the legume subfamilies Caesalpinioideae and Papilionoideae. To understand the relationship between the cell number and size in the petals of zygomorphic flowers, the comparative morphology and anatomy of flower petals were examined in Cercis chinensis and Caesalpinia decapetala var. japonica in Caesalpinioideae, and Lespedeza formosa subsp. velutina and Pueraria lobata in Papilionoideae. Increased petal size is correlated to a higher number and/or size of the cells of the petal in Caesalpinioideae. The characteristics flower morphology of the Papilionoideae has evolved by increased cell numbers, although the cell size was the smallest. Papilionoideae has characteristic papilionoid flowers consisting of five specialised petals. These characteristic morphologies were generated from the complicated changing pattern of cells in petals in the course of legume diversification.

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