'Isabel Pierce' is a Diploid

Rhododendron 'Isabel Pierce', which is a Lawrence Pierce hybrid documented as 'Anna' x 'Lem's Goal', 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 'Anna',
Diploid 'Isabel Pierce',
Diploid 'Norman Gill',
Diploid 'The Honorable Jean Marie de Montague'

Source: Greer Gardens

John and Sally Perkins