Comparative development of perianth and androecial primordia of the single flower and the homeotic double-flowered mutant in Hibiscus rosa-sinensis (Malvaceae)

Homeosis is defined as the complete or partial replacement of one part of an organism with another part. Double-flowered cultivars of H. rosa-sinensis display a divergent floral morphology that appears to fit the criteria for homeosis. The corolla of single flowered cultivars is pentamerous. Mature flowers have a staminal tube bearing 60-70 stamens that surrounds an exserted synstylous gynoecium with 5 fused stigmas. In double flowers, the outermost whorl of petals is similar in appearance to that of single flowers. The remaining floral appendages have a morphology that is intermediate between petals and stamens, to varying degrees. No 2 double 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 single flowers, petal primordia are initiated on the flank of the ring, and then stamen primordia arise in 5 distinct and orderly clusters. In double flowers, petal primordia are also initiated on the abaxial flank, but the remainder of the ring initiates primordia that form a mixture of petals, petal-stamen intermediates and stamens. A common ring meristem that has 2 different developmental pathways provides a novel opportunity to study homeosis from the perspective of comparative developmental morphology..