Rhododendron 'Opal Thornton', which is a John Thornton hybrid documented as 'Antoon van Welie' x R. hyperythrum, 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.
John Thornton's Breeding Rhododendrons for the Gulf South
Summary of Ploidy Levels
Triploid 'Opal Thornton',
Tetraploid 'Antoon van Welie'
Source: Rarefind Nursery
John and Sally Perkins
