Rhododendron 'Harrison's Red', which is a documented as Rhododendron austrinum, has been determined to be a triploid 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 results suggests that 'Harrison's Red' is a Rhododendron austrinum hybrid rather than a color form of the straight species.
Rhododendron Species Foundation lists 'Harrison's Red' under Rhododendron austrinum as follows:
1993/002 'Harrison's Red' A floriferous and easily grown deciduous azalea with slightly fragrant flowers in mid-spring. The flower color on this selection is listed as "rosy-red" but I have not recorded it in flower. Very heat tolerant, sun or shade. (-10\R1\6)
Summary of Ploidy Levels
Triploid 'Evening Sun',
Triploid 'Harrison's Red',
Tetraploid Rhododendron austrinum
Source: Woodlanders Nursery
John and Sally Perkins
