'Electum' is a Tetraploid

Rhododendron 'Electum', which is a 1850 Standish and Noble Ghent hybrid, 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.

Summary of Ploidy Levels

Diploid 'Miniatum Floribundum',
Triploid 'Aida',
Triploid 'Bronze Unique',
Triploid 'Croceum Tricolor',
Triploid 'Daviesii',
Triploid 'Deep Rose',
Triploid 'Freya',
Triploid 'Gloria Mundi',
Triploid 'Il Tasso',
Triploid 'Josephine Klinger',
Triploid 'Phebe',
Triploid 'Phidias',
Triploid 'Pontica Album',
Triploid 'Van Houttei Flore Pleno',
Triploid 'Velasquez',
Tetraploid 'Admiraal De Ruyter',
Tetraploid 'Altaclerensis',
Tetraploid 'Ariel',
Tetraploid 'Beaté Céleste',
Tetraploid 'Bijou des Amateurs',
Tetraploid 'Bouquet de Flore',
Tetraploid 'Cardinal,
Tetraploid 'Comte de Flandre',
Tetraploid 'Corneille',
Tetraploid 'Directeur Charles Baumann',
Tetraploid 'Durante Alle',
Tetraploid 'Electum',
Tetraploid 'Eugénie',
Tetraploid 'Fénelon',
Tetraploid 'Flameola Incarnata',
Tetraploid 'Héroine Plena,
Tetraploid 'Heureuse Surprise',
Tetraploid 'Ignacea',
Tetraploid 'Julius Caesar',
Tetraploid 'Lelia',
Tetraploid 'Madame Gustave Guillemot',
Tetraploid 'Nancy Waterer',
Tetraploid 'Oscar I',
Tetraploid 'Raphael de Smet'

Source: Azaleatuin

John and Sally Perkins

'Cynthia' is a Fertile Triploid

Rhododendron 'Cynthia', which is a 1856 Standish and Noble hybrid documented as R. catawbiense x R. griffithianum, 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.

'Cynthia' is the pollen parent of 'Countess of Derby'. M. Stockman used 'Cynthia' as a seed or pollen parent in several of his crosses.

'Countess of Derby', which has 'Pink Pearl' and 'Cynthia' as parents and 'Broughtonii' as an ancestor, is a cross between 2 fertile triploids.

Summary of Ploidy Levels

Triploid 'Broughtonii',
Triploid 'Cynthia',
Tetraploid 'Countess of Derby'

Source: Whitney Nursery

John and Sally Perkins