'Consul Pecher' is a Diploid

Rhododendron 'Consul Pecher', which is a Rhododendron molle hybrid, has been determined to be a diploid using flow cytometry by

Dr. João Loureiro, Dr. Silvia Castro, José Cerca Oliveira, 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 Rhododendron molle,
Diploid 'Consul Pecher'

Source: Arnold Arboretum Accession Number: 837-59

John and Sally Perkins

"(viscosum X arborescens) not" is a Tetraploid

Two plants labeled Rhododendron viscosum X Rhododendron arborescens have been determined to be a tetraploid using flow cytometry by

Dr. João Loureiro, Dr. Silvia Castro, José Cerca Oliveira, 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.

The ploidy test indicates this plant may instead contain Rhododendron atlanticum. Both of thedse plants were raised by George Hibben.

Summary of Ploidy Levels

Diploid Rhododendron viscosum,
Diploid Rhododendron arborescens,
Tetraploid Rhododendron atlanticum,
Tetraploid "(Rhododendron viscosum X Rhododendron arborescens) not"

Source: Arnold Arboretum Accession Number: 139-98-A
Source: George Hibben

John and Sally Perkins

atlanticum X caledulaceum is a Tetraploid

[Rhododendron atlanticum X Rhododendron calendulaceum] "Broken Arrow", which is a Dick Jaynes hybrid, has been determined to be a tetraploid using flow cytometry by

Dr. João Loureiro, Dr. Silvia Castro, José Cerca Oliveira, 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

Tetraploid Rhododendron atlanticum,
Tetraploid Rhododendron calendulaceum,
Tetraploid Rhododendron atlanticum X Rhododendron calendulaceum "Broken Arrow",
Tetraploid Rhododendron atlanticum X Rhododendron calendulaceum orange,
Tetraploid Rhododendron atlanticum X Rhododendron calendulaceum pink

Source: Arnold Arboretum Accession Number: 410-2002

John and Sally Perkins

Rhododendron luteum is a Tetraploid

Rhododendron luteum 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.

Rhododendron luteum was also determined to be a tetraploid using flow cytometry by Dr. Thomas Ranney, J.R. Jones, and Nathan Lynch.

Summary of Ploidy Levels

Tetraploid Rhododendron luteum,
Tetraploid Rhododendron luteum 'Golden Comet',
Tetraploid Rhododendron luteum Orange form,
Tetraploid Rhododendron luteum Yellow form

Source: Arnold Arboretum
Source: John and Sally Perkins
Source: Kristian Theqvist

John and Sally Perkins

"Gladywense" is a Triploid

Rhododendron "Gladywense" 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.

Summary of Ploidy Levels

Triploid Rhododendron "Gladywense"

Source: Arnold Arboretum Accession Number: 979-67-A

John and Sally Perkins

Rhododendron "calendulaceum not" is a Triploid

Rhododendron "calendulaceum not", which appears to be a hybrid between Rhododendron flammeum and Rhododendron calendualceum, 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.

Summary of Ploidy Levels

Diploid Rhododendron flammeum,
Triploid Rhododendron "calendulaceum not",
Tetraploid Rhododendron calendualceum

Source: Arnold Arboretum Accession Number: 109-2007-Y

John and Sally Perkins

'Unique' is a Triploid?

Rhododendron 'Unique', which is a Ghent 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 'Unique' was determined to be a tetraploid using flow cytometry by Tom Eeckhaut.

Summary of Ploidy Levels

Triploid 'Unique'

Source: Arnold Arboretum Accession Number: 72-57-B

John and Sally Perkins

Rhododendron viscosum forma rhodanthum is a Diploid

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

Rhododendron calendulaceum var. croceum is a Tetraploid

Rhododendron calendulaceum var. croceum 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.

Rhododendron calendulaceum was also determined to be a tetraploid using flow cytometry by Dr. Thomas Ranney, J.R. Jones, and Nathan Lynch.

Summary of Ploidy Levels

Tetraploid Rhododendron calendulaceum,
Tetraploid Rhododendron calendulaceum var. croceum,
Tetraploid Rhododendron calendulaceum 'Cherokee',
Tetraploid Rhododendron calendulaceum 'Smoky Mountaineer'

Source: Arnold Arboretum Accession Number: 17758-1-A

John and Sally Perkins

Rhododendron prunifolium is a Diploid

Rhododendron prunifolium 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.

Summary of Ploidy Levels

Diploid Rhododendron prunifolium,
Diploid Rhododendron prunifolium 'David Ellis'

Source: Arnold Arboretum Accession Number: 85-D
Source: Connecticut College Arboretum Accession Number: 83-39-A

John and Sally Perkins

Rhododendron calendulaceum 'Smoky Mountaineer' is a Tetraploid

Rhododendron calendulaceum 'Smoky Mountaineer' 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

Tetraploid Rhododendron calendulaceum,
Tetraploid Rhododendron calendulaceum var. croceum,
Tetraploid Rhododendron calendulaceum 'Cherokee',
Tetraploid Rhododendron calendulaceum 'Smoky Mountaineer'

Source: Arnold Arboretum Accession Number: 22690

John and Sally Perkins

'Cymodocee' is a Tetraploid

Rhododendron 'Cymodocee', which is a 1900 C. Vuylsteke 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',
Triploid/Tetraploid 'Praxitèle',
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 'Cymodocee',
Tetraploid 'Directeur Charles Baumann',
Tetraploid 'Durante Alle',
Tetraploid 'Electum',
Tetraploid 'Eugénie',
Tetraploid 'Fénelon',
Tetraploid 'Flameola Incarnata',
Tetraploid 'Héroine Plena,
Tetraploid 'Heureuse Surprise',
Tetraploid 'Hollandia',
Tetraploid 'Hora',
Tetraploid 'Ignacea',
Tetraploid 'Igneum Novum',
Tetraploid 'Il Tasso',
Tetraploid 'Jenny Lind',
Tetraploid 'Juliana Nova',
Tetraploid 'Julius Caesar',
Tetraploid 'Leibuir',
Tetraploid 'Lelia',
Tetraploid 'Madame Gustave Guillemot',
Tetraploid 'Marie Verschaffelt',
Tetraploid 'Minerva',
Tetraploid 'Nancy Waterer',
Tetraploid 'Oscar I',
Tetraploid 'Perfecta',
Tetraploid 'Princesse d' Orange',
Tetraploid 'Quentin Metsys',
Tetraploid 'Racine',
Tetraploid 'Ribera',
Tetraploid 'Raphael de Smet',
Tetraploid 'Rose Marie',
Tetraploid 'Souvenir du Président Carnot'.
Tetraploid 'Teniers'

Source: Arnold Arboretum Accession Number: 17121-A

John and Sally Perkins

Arnold Arboretum Living Collection

Our ploidy research has included the testing of samples from the Living Collection of the Arnold Arboretum.

The "In The Collections" web page of the Arnold Arboretum includes a reference to our ploidy research.

John and Sally Perkins

'Lelia' is a Tetraploid

Rhododendron 'Lelia', which is a 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.

To date, all Ghent deciduous azaleas have tested as triploid or tetraploid.

Summary of Ploidy Levels

Triploid 'Bronze Unique',
Triploid 'Daviesii',
Triploid 'Deep Rose',
Triploid 'Gloria Mundi',
Triploid 'Josephine Klinger',
Tetraploid 'Bijou des Amateurs',
Tetraploid 'Comte de Flandre',
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: Arnold Arboretum Accession Number: 572-58

John and Sally Perkins

'Bijou des Amateurs' is a Tetraploid

Rhododendron 'Bijou des Amateurs', which is a 1860 Baumann 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.

To date, all Ghent deciduous azaleas have tested as triploid or tetraploid.

Summary of Ploidy Levels

Triploid 'Bronze Unique',
Triploid 'Daviesii',
Triploid 'Deep Rose',
Triploid 'Gloria Mundi',
Triploid 'Josephine Klinger',
Tetraploid 'Bijou des Amateurs',
Tetraploid 'Comte de Flandre',
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 Arnold Arboretum Accession Number: 17100

John and Sally Perkins

Rhododendron Xanneliesae is a Tetraploid

Rhododendron Xanneliesae, which was received by the Arnold Arboretum in 1921 from Hunnewell Pinetum documented to be a Rhododendron arborescens / Rhododendron calendualceum interaction, 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.

Rhododendron Xanneliesae is very seed fertile.

Rhododendron calendulaceum is a tetraploid species. Rhododendron arborescens is a diploid species.

Diploid / tetraploid interaction in deciduous azaleas normally results in triploid offspring.

"A monograph of azaleas: Rhododendron subgenus Anthodendron" By Ernest Henry Wilson, Alfred Rehder

"This hybrid originated accidentally at the Arnold Arboretum and was raised probably in 1896 from seed of R. calendulaceum or R. arborescens collected in the Arboretum. It is exactly intermediate between R. calendulaceum and R. arborescens and I have little doubt that it is a hybrid between these two species. The first flowers of R. arborescens are usually just beginning to open about the middle of June when late blooming forms of R. calendulaceum bear the last flowers; and with dichogamous plants this is just a favorable condition for cross-fertilization. From R. calendulaceum it differs chiefly in the glaucous and glabrous under side of the leaves, only the midrib being furnished with strigose hairs and slightly pubescent toward the base, in the very sparingly hairy branchlets and in the longer corollatube of the pinkish white fragrant flowers marked with a large yellow blotch and in the style puberulous only near the base. From R. arborescens it differs in the slightly pilose and slightly puberulous branchlets, glabrescent toward the base, in the pubescent and strigose midrib of the under side of the leaves, in the large yellow blotch on the upper lobe of the pinkish white flowers, in the shorter ovate calyx-lobes and in the style being puberulous near the base.

It is a shrub of vigorous habit, very handsome in flower with its large fragrant, pinkish white flowers marked with a conspicuous yellow blotch; the pinkish corollatube is rather densely furnished with short glandular hairs and the style is purple toward the apex. The leaves are elliptic or broadly elliptic and somewhat bluish green above."

Summary of Ploidy Levels

Diploid Rhododendron arborsecens,
Tetraploid Rhododendron Xanneliesae,
Tetraploid Rhododendron calendulaceum

Source: Arnold Arboretum Accession Number: 10767

John and Sally Perkins

Rhododendron calendulaceum X molle is a Tetraploid

Rhododendron calendulaceum X Rhododendron molle, which was received by the Arnold Arboretum in 1921 from Hunnewell Pinetum, 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.

Rhododendron calendulaceum is a tetraploid species. Rhododendron molle is a diploid species.

Tetraploid deciduous azaleas normally reject pollen from diploid deciduous azaleas. Diploid / tetraploid interaction in deciduous azaleas normally results in triploid offspring.

Listing the parentage of a cross alphabetically is not uncommon especially prior to 1930. In the literature, Rhododendron molle, which is a species, is frequently confused with Mollis which is a reference to deciduous azaleas hybrids containing Rhododendron molle.

Summary of Ploidy Levels

Diploid Rhododendron molle,
Tetraploid Rhododendron calendulaceum X Rhododendron molle,
Tetraploid Rhododendron calendulaceum

Source: Arnold Arboretum Accession Number: 10768

John and Sally Perkins

'Brazil' is a Tetraploid

Rhododendron 'Brazil', which is a Exbury, 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

Tetraplid 'Brazil',
Tetraploid 'Embley Crimson'

Source: Arnold Arboretum Accession Number: 628-61

John and Sally Perkins

'Embley Crimson' is a Tetraploid

Rhododendron 'Embley Crimson', which is a 1965 Knaphill, 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

Tetraplid 'Brazil',
Tetraploid 'Embley Crimson'

Source: Arnold Arboretum Accession Number: 1230-65-C

John and Sally Perkins

'Heureuse Surprise' is a Tetraploid

Rhododendron 'Heureuse Surprise', which is a 1855 Sunningdale Nursery 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.

To date, all Ghent deciduous azaleas have tested as triploid or tetraploid.

Summary of Ploidy Levels

Triploid 'Bronze Unique',
Triploid 'Daviesii',
Triploid 'Deep Rose',
Triploid 'Gloria Mundi',
Triploid 'Josephine Klinger',
Tetraploid 'Bijou des Amateurs',
Tetraploid 'Comte de Flandre',
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: Arnold Arboretum Accession Number: 7105

John and Sally Perkins