Species In Our Midst
Rhododendron prinophyllum

Rhododendron prinophyllum
Picture by S & J Perkins

Roseshell Rhododendron (synonyms: Mayflower Azalea, Rosy Pinxterbloom)

Epithet

With leaves like Prinos. Prinos from the Greek meaning oak, or prinos meaning winterberry (Prinos verticillata Linn now Ilex verticillata).

History

The first reference I could find is a Cherokee Indian legend, ancient before the first Europeans reached our shores. After that, R. prinophyllum was mentioned as a variety of Azalea nudiflora in 1787 by Wangenheim who found it in New York State.

• 1812 The species was introduced but was in cultivation in Europe before that, perhaps introduced by Peter Collinson for whom the American John Bartram collected.
• 1830 Identified as Rhododendron nudiflorum var. roseum (Sweet)
• 1836 Identified as Rhododendron nudiflorum (Darlington)
• 1914 Identified as Azalea prinophylla by Small in North America Flora
• 1921 Identified as Rhododendron roseum(Rheder)
• 1922 Sargent sent seeds to Britain from the U.S.
• 1926 Identified as Azalea nudiflora var. rosea (Sweet)
• 1955 Rhododendron roseum received an Award of Merit when exhibited by Mrs. R. M. Stevenson at Tower Court, Ascot
• As late as 1965, F. P. Lee in The Azalea book speaks of the Roseum Nudiflorum Alliance in which he includes R. canescens, R. nudiflorum (periclymenoides), R. occidentale, and R. roseum (prinophyllum).

Distribution

R. prinophyllum is native to open woods from southwestern Quebec to the mountains of Virginia, west to Missouri and northern Indiana and in the East, Massachusetts, Vermont, Pennsylvania, and New York. The purest forms the least contaminated by hybridization are found in the Blue Ridge Mountains of Virginia.

Hardiness

Zone 3 to -25°F or lower regularly to -40°F in Bellows Falls and Saxon River, Vermont.

Description

R. prinophyllum is similar morphologically to both R. periclymenoides and R. canescens, sympatric with R. periclymenoides but isolated geographically from R. canescens.

R. prinophyllum is a shrub 2'-8' rarely to 15' high, rarely stoloniferous. The leaves are bluish green 3-7 cm long. The new growth and floral and winter buds are densely pubescent and both surfaces of true leaves somewhat villous. The leaves are deciduous and elliptic. The inflorescence is terminal with 5-9 flowers opening in May with the leaves. The flowers, which may be pink, purplish pink or rarely white, are strongly clove-scented. The calyx is 5 lobed, the corolla funnel shaped with 5 stamens 3-5 cm long. The ovary is 5 celled and moderately glandular, the capsule oblong and minutely glandular, and the calyx persistent.

Hybrids

R. prinophyllum has been used for hybridizing where both extreme hardiness and fragrance are desired.

Abbott Hybrids developed by Frank Abbot of Vermont and by Weston Nurseries include

• 'Frank Abbott' prinophyllum x a red mollis selection
• 'Jane Abbott'
• 'Peach Abbott' mildew resistant with good fall color
• 'Margaret Abbott' prinophyllum x calendulaceum

'Marie Hoffman', a selected clear pink clone selected by Lud Hoffman. It is perhaps a tetraploid.

Northern Lights Series developed by Albert G. Johnson in the late 1930's and Harold Pellett of the University of Minnesota starting in 1957. The first four to be introduced were:

• 'White Lights' and 'Spicy Lights', both prinophyllum x Exbury hybrids
• 'Pink Lights' and 'Rosy Lights', both crosses between (Rhododendron x kosteranum) x Rhododendron prinophyllum
• These have been followed by 'Northern Hi-Lights', 'Apricot Surprise', and 'Golden Lights'. All are extremely hardy with flower buds able to withstand winter temperatures of -45°F without injury. All have pleasant fragrance inherited from R. prinophyllum.

There is a list of 13 azaleas bred by Frank Abbott, crosses of R. calendulaceum and R. japonicum with R. prinophyllum, that were selected by Bob Carlson for sale at his nursery in New York State. All are hardy to -25°F. They are no longer listed in his latest, 1996 catalogue.

• 'Abbott's Orange Glow'
• 'Gold Chip'
• 'Abbott's Rose Ruffles'
• 'Sparkle Plenty'
• 'Bit O'Honey '
• 'Starfire'
• 'Coral Sands'
• 'Starlight'
• 'Doing My Thing'
• 'Strawberry Blond'
• 'Double Dip'
• 'Vermont Gold'
• 'White Star'

References

• Edinburgh Journal of Botany. Vol. 50, #3 1993
• The Azalea Book. F. P. Lee. 2nd Edition. 1965
• Rhododendrons and Azaleas. Clement Gray Bowers.2nd Edition. 1960
• Azaleas. Fredrick Street. 1959
• Great American Azaleas. Jim Darden. 1985
• Colonial Gardens. Favrelli and DeWolf. 1972
• Rhododendrons and American Plants. Edward Sprague Rang. 1871
• The Rhododendron Species. Vol. IV Azaleas. Davidian. 1995
• Manual of Cultivated Trees and Shrubs. Rehder. 2nd Edition. 1940
• New Cyclopedia of American Horticulture. L. H. Bailey. 1906