Morphological and transcriptomic analyses of merism variation in azalea

Merism (the number or organs per whorl) is a primary characteristic of ornamental value and evolutionary differences for flowering plants, but the molecular mechanism that controls the merism rule remains unclear.
Merism is relatively fixed, and usually occurs as five or multiples of five organs per whorl (also named pentamerous flower) for azaleas, the famous woody ornamentals of the temperate zone.
However, simultaneous existence of merism variation with tetramerous/ pentamerous/hexamerous flowers was found on the same branch of Rhododendron ovatum, one azalea species that has high ornamental value with elegant mauve flowers and pleasant fragrance.
These isomerous changes affect all organ whorls of a flower, that is the number of organs (including sepal, petal, stamen, and carpel) increase to six or decrease to four.
Transcriptomic analyses of different merisms were conducted to characterize the mechanisms of the merism variation in R. ovatum. Genes related to flower development or number, such as MADS-box family, CLAVATA, PERIANTHA, ULTRAPETALA, and CYCLOIDEA, were analyzed at the whole genome-wide level and demonstrate their potential contribution to merism variation.
This research laid the foundation for the characteristics of merism in azalea and will contribute to the evolutionary study of merism variation in different clades of angiosperms.

V International Symposium on Woody Ornamentals of the Temperate Zone

X. Wang, M. Liu, Y. Cao, Q. Wang, H. Zhou, Y. Xia

organs per whorl, Rhododendron ovatum, isomerous change, floral organ, MADS

https://doi.org/10.17660/ActaHortic.2025.1434.23