"(flammeum X calendulaceum) not" is a Diploid

Rhododendron "(flammeum X calendulaceum) not", which is a John Thornton 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.

Ploidy testing indicates that Rhododendron calendulaceum may not be the pollen parent of this hybrid.

Summary of Ploidy Levels

Diploid Rhododendron flammeum,
Diploid "(flammeum X calendulaceum) not",
Tetraploid Rhododendron calendulaceum

Source: John Thronton

John and Sally Perkins

'English Roseum' X [diaprepes X hyperthrum] is a Diploid

Rhododendron 'English Roseum' X [Rhododendron diaprepes X Rhododendron hyperthrum], which is a Thornton hybrid, 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 diaprepes 'Gargantua', which is a tetraploid, may have been one of the parents in the cross of Rhododendron diaprepes X Rhododendron hyperthrum. Neotetraploids and triploids can produce diploid offspring.

Rhododendron diaprepes is most likely a diploid species.

Summary of Ploidy Levels

Diploid Rhododendron 'English Roseum' X [Rhododendron diaprepes X Rhododendron hyperthrum],
Tetraploid Rhododendron diaprepes 'Gargantua'

Source: John Thornton

John and Sally Perkins

'Sham's Ruby' X 'J.L. Creech' is a Diploid

Rhododendron 'Sham's Ruby' X 'J.L. Creech', which is a Thornton hybrid, 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 'Sham's Ruby' X 'J.L. Creech'

Source: John Thornton

John and Sally Perkins

'Bibiani' X 'J.L. Creech' is a Diploid

Rhododendron 'Bibiani' X 'J.L. Creech', which is a Thornton hybrid, 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 'Bibiani',
Diploid 'Bibiani' X 'J.L. Creech'

Source: John Thornton

John and Sally Perkins

'Will O The Wisp' is a Diploid

Rhododendron 'Will O The Wisp', which is a John Thornton hybrid documentd as Rhododendron minus X Rhododendron formosum, 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 minus is a diploid species.

Summary of Ploidy Levels

Diploid Rhododendron minus,
Diploid 1 seedling from Rhododendron formosum X Rhododendron minus,
Diploid 'Will O The Wisp'

Source: John Thornton

John and Sally Perkins

Rhododendron formosum X Rhododendron minus is a Diploid

One seedling of Rhododendron formosum X Rhododendron minus, which is a John Thornton hybrid, 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 minus is a diploid species.

Summary of Ploidy Levels

Diploid Rhododendron minus,
Diploid 1 seedling from Rhododendron formosum X Rhododendron minus,
Diploid 'Will O The Wisp'

Source: John Thornton

John and Sally Perkins

Rhododendron prunifolium X Rhododendron austrinum is a Triploid

One seedling of Rhododendron prunifolium X Rhododendron austrinum, which is a John Thornton 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 prunifolium is a diploid species. Rhododendron austrinum is a tetraploid species.

In this case of this triploid (39 chromosomes), a diploid crossed with a tetraploid produced a triploid indicating normal meiosis occurred where the diploid contributed a 1x gamete (13 chromosomes) and the tetraploid contributed a 2x gamete (26 chromosomes).

Summary of Ploidy Levels

Diploid Rhododendron prunifolium,
Triploid 1 seedling from Rhododendron prunifolium X Rhododendron austrinum,
Tetraploid Rhododendron austrinum

Source: John Thornton

John and Sally Perkins

Rhododendron viscosum X Rhododendron austrinum is a Triploid

One seedling of Rhododendron viscosum syn. serrulatum X Rhododendron austrinum, which is a John Thornton 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 viscosum is a diploid species. Rhododendron austrinum is a tetraploid species.

In the case of this triploid (39 chromosomes), a diploid crossed with a tetraploid produced a triploid indicating normal meiosis occurred where the diploid contributed a 1x gamete (13 chromosomes) and the tetraploid contributed a 2x gamete (26 chromosomes).

Rhododendron viscosum syn. serrulatum is sometimes documented as Rhododendron serrulatum but is now considered merely a southern form of Rhododendron viscosum

Summary of Ploidy Levels

Diploid Rhododendron viscosum,
Triploid 1 seedling from Rhododendron viscosum syn. serrulatum X Rhododendron austrinum,
Tetraploid Rhododendron austrinum

Source: John Thornton

John and Sally Perkins

'Opal Thornton' is a Triploid

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