One seedling of Rhododendron viscosum syn. serrulatum X Rhododendron austrinum, which is a John Thornton hybrid, has been determined to be a triploid using flow cytometry by
Dr. João Loureiro, Dr. Silvia Castro, José Cerca, and Mariana Castro
Plant Ecology and Evolution Group,
Centre for Functional Ecology,
Department of Life Sciences,
Faculty of Science and Technology,
University of Coimbra, Portugal.
Rhododendron viscosum is a diploid species. Rhododendron austrinum is a tetraploid species.
In the case of this triploid (39 chromosomes), a diploid crossed with a tetraploid produced a triploid indicating normal meiosis occurred where the diploid contributed a 1x gamete (13 chromosomes) and the tetraploid contributed a 2x gamete (26 chromosomes).
Rhododendron viscosum syn. serrulatum is sometimes documented as Rhododendron serrulatum but is now considered merely a southern form of Rhododendron viscosum
Summary of Ploidy Levels
Diploid Rhododendron viscosum,
Triploid 1 seedling from Rhododendron viscosum syn. serrulatum X Rhododendron austrinum,
Tetraploid Rhododendron austrinum
Source: John Thornton
John and Sally Perkins
