5 plants of Rhododendron subulatum from China growing at the Arnold Arboretum 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 subulatum was formerly classified as subspecies of Ledum palustre.
The 5 plants of Rhododendron subulatum tested as diploid were from northern China.
A Rhododendron tomentosum wild collected from a marsh in Turku Archipelago, Finland tested as tetraploid.
There is a very good chance that this difference in ploidy level is due to misidentification of the plant from China due to the large group of plants formerly included under Ledum palustre and then compounded when the Ledum genus was moved to Rhododendron.
The plant from China is clearly a diploid "Ledum". The origin of the plant tested is well documented. This plant is still growing at the Arnold Arboretum along with 4 of its siblings.
Summary of Ploidy Levels
Diploid Rhododendron columbianum,
Diploid Rhododendron subarticum,
Diploid 5 plants of Rhododendron subulatum China,
Tetraploid Rhododendron diversipilosum,
Tetraploid Rhododendron diversipilosum 'Milky Way',
Tetraploid Rhododendron groenlandicum,
Tetraploid Rhododendron groenlandicum Saco Bog, Maine,
Tetraploid Rhododendron hypoleucum,
Tetraploid Rhododendron neoglandulosum,
Tetraploid Rhododendron tolmachevii,
Tetraploid Rhododendron tomentosum Turku Archipelago
Source: Arnold Arboretum Accession Number: Ledum palustre 389-97-A,B,C,D,E Wild collected in China
John and Sally Perkins
