COMPARATIVE DEVELOPMENT OF PERIANTH AND ANDROECIAL PRIMORDIA OF THE SINGLE FLOWER AND THE HOMEOTIC DOUBLE-FLOWERED MUTANT IN HIBISCUS-ROSA-SINENSIS (MALVACEAE)

The double-flowered variety of Hibiscus rosa-sinensis L. (Malvaceae) d isplays a divergent floral morphology that appears to fit the criteria for homeosis. A comprehensive definition defines homeosis as the comp lete or partial replacement of one part of an organism with another pa rt. The corolla of the single flower is pentamerous. The mature flower has a staminal tube bearing 60-70 stamens that surrounds an exserted synstylous gynoecium with five fused stigmas. In double flowers, the o utermost whorl of petals is similar in appearance to that of the singl e flower. The remaining floral appendages have a morphology that is in termediate between petals and stamens, to varying degrees. No two doub le flowers are exactly the same, even on the same plant. As with other members of the Malvaceae, floral development in both floral types is unusual: once the calyx has been initiated, a ring meristem is formed from which both petal and stamen primordia are initiated. In the singl e flower, petal primordia are initiated on the flank of the ring, and then stamen primordia arise in five distinct and orderly clusters. In the double flower, petal primordia are also initated on the abaxial fl ank, but the remainder of the ring initiates primordia that form a mix ture of petals, petal-stamen intermediates, and stamens. A common ring meristem that has two different developmental pathways provides a nov el opportunity to study homeosis from the perspective of comparative d evelopmental morphology.