Rhododendron 'Briggs Red Star', which is a chemically treated 'The Honourable Jean Marie de Montague' produced by Briggs, has been determined to be a tetraploid 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.
Ranney, Jones, and Lynch found 'Brigg's Red Star' to be a 2x + 4x mixaploid which breeds as a tetraploid having tetraploid pollen.
Summary of Ploidy Levels
Diploid 'The Honourable Jean Marie de Montague',
Tetraploid 'Brigg's Red Star'
Source: Ned Brockenbrough
John and Sally Perkins
