Rhododendron viscosum forma rhodanthum has been determined to be a diploid 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 forma rhodanthum appears to be a natural hybrid most likely containing Rhododendron cumberlandense.
Rhododendron viscosum was also determined to be a diploid using flow cytometry by Dr. Thomas Ranney, J.R. Jones, and Nathan Lynch.
Summary of Ploidy Levels
Diploid Rhododendron cumberlandense,
Diploid Rhododendron viscosum,
Diploid Rhododendron viscosum forma rhodanthum,
Diploid Rhododendron viscosum var. serrulatum
Source: Arnold Arboretum Accession Number: 638-62
John and Sally Perkins