Comparative morphology of single and double flowers in Hibiscus rosa-sinensis L. (Malvaceae): A homeosis study

Abstract

Hibiscus rosa-sinensis L. is known as an ornamental plant due to the variety of its flowers. Generally, H. rosa-sinensis L. has two distinct floral forms: single and double flowers. In double flowers, stamens are replaced by petals which are known as homeosis, a phenomenon in the plant that referred as a complete or partial replacement of one structure into another structure. Study on homeosisusing single and double flower has been reported in H. rosa-sinensis L. However, we found two other types of double flower in the same species. Hence, this study was conducted to give an insight of homeosis based on morphological observation in H. rosa-sinensis L. According to gross morphology in 12 varieties of H. rosa-sinensis L. used in this study, we divided double flower into 3 types, namely as type I, type II and type III. In all double flowers, the outermost whorl of petals is similar in appearance to that of the single flower. The single flower and the 3 types of double flower differ interms of an additional petals, stamen number, and carpel. The single flowers have 5 petals and 46--101 stamens. The type I double flowers have 0--44 stamens and additional petals, which are 7--28 staminodium petaloid and 1—21 stamen-petal intermediate. The type II double flowers have 3--88 stamens, 5--36 staminodium petaloid, and 0--7 stamen-petal intermediate, while the type III double flowers have 54--105 stamens, 22--36staminodium petaloid, and 0--5 stamen-petal intermediate. In type III double flowers, carpel organs turn into petal-like structures, while in type I and II carpels still exist and similar with those found in single flowers. Since the homeosis is regulated by ABC homeotic genes, we may relate an inward shifting of stamens or carpels into petal-like structures due to restriction of C gene (AGAMOUS) expression or other cadastral regulators that need further investigation.