CPC Plant Profile: Pink-shell Azalea
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Plant Profile

Pink-shell Azalea (Rhododendron vaseyi)

A closeup of the the pink flowers of this species, with 5-7 stamen and a short (2 - 5 mm long) corolla tube. Photo Credit: Tom Ward
Description
  • Global Rank: G3 - Vulnerable
  • Legal Status: N/A
  • Family: Ericaceae
  • State: CT, MA, NC
  • Nature Serve ID: 142664
  • Date Inducted in National Collection: 01/01/1985

Rhododendron vaseyi is a deciduous, upright narrow shrub that can grow to 5 meters in height with appealing erect branches (Wilson and Rehder 1921, Cox 1990) Its root system is compact and shallow. Scentless, pinkish white flowers begin blooming in April and are thought to attract hummingbirds (Radford et al. 1968, Dirr 1998, Hightshoe 1988, Foote and Jones 1994). This peculiar endemic of the Blue Ridge was found in 1878 in western North Carolina by G. R. Vasey, son of the government botanist, G. Vasey, and named after its discoverer (Bensley 2002). The first plant was acquired for cultivation by the Arnold Arboretum in 1880.

Participating Institutions
Updates
  • 10/16/2020
  • Propagation Research

Apparently, R. vaseyi does not hybridize and stays stable when grown from seed. Propagation from seed: sow into milled Sphagnum, maintain humidity under cover, water carefully. Seedlings are tiny and growing slowly. Put them a few per pot first, to reduce the risk of overwatering; repot once they achieve sufficient size. Propagation from softwood cuttings: take cuttings in May-June, keep them under fog or mist in 50/50 sand-perlite. With 2,500-5,000 ppm K-IBA or H # 3 treatment, the rooting rate is 70-80%. Cuttings become more secure once they survive through the first winter.

  • 10/16/2020
  • Living Collection

As part of its commitment to the Center for Plant Conservation (CPC), the Arnold Arboretum of Harvard University maintains and develops its collection of Rhododendron vaseyi. Our primary goal is to preserve the highest level of intraspecific diversity as is practicable and provide access to researchers, educators, and the general public. In 2018, our Rhododendron vaseyi collection includes: 26 accessions representing 26 distinct lineages, 4 plants growing in our nursery, and 41 plants growing outdoors in the living collections. Each plant within an accession is maintained individually, separated by provenance, and their placement in the landscape (10 distinct locations within the 281 acre landscape) ensures individual populations/genetics remain separate.

Kathryn Richardson
  • 02/09/2018

The Arboretum manages the Rhododenron vaseyi collection by: practicing world class horticulture, acquiring and maintaining detailed plant records collecting herbarium specimens, harvesting and drying leaves for DNA extraction, capturing digital images. An important part of our mission is to provide access to the living collections (germplasm and related information) to researchers around the world. We both welcome scholars to visit and conduct research onsite at the Arnold Arboretum as well as collaborate globally collecting and shipping samples around the world.
 
Each Living Collections department plays an important role in managing the collection:
 
Horticulture Staff

  • Responsibilities include planting and transplanting plants from the nursery to the grounds, turf care, monitoring for insects and diseases, applying pesticides and biological controls, pruning, removing dead or declining trees, chipping brush, watering, fertilizing, applying soil amendments, removing volunteer plants and invasives, rejuvenating planting beds, mulching, removing litter, plowing snow, and maintaining equipment.
  • The Arboretum’s Landscape Management Plan divides the Arboretum into 71 zones based on location, environmental characteristics, and collections. Each horticulturist is responsible for a set of zones, allowing them to become experts on their particular zones and improve the quality of the care they provide. High value collections, such as Rhododendron vaseyi, are highlighted within each zone.
  • Maintains the Rhododendron vaseyi collection as individual specimens.
Curatorial Staff
  • Perform field checks in accordance with the Plant Inventory and Operations Manual [pdf]. This includes databasing health and performance observations for the entire collection, identity verification, label need assessment, and mapping (GIS).
  • Deposit herbarium specimens (vegetative, flower and fruit) for each accession in the living collections to the Herbarium of Cultivated Plants. Management and development of the collection is guided by the Cultivated Herbarium Collections Policy [pdf].
  • Provide access to the living collections for research and educational purposes. This includes access to plant material, sharing of germplasm, access to the landscape for frequent observations and experiments, and access to plant records (historic and present).
  • Acquire germplasm for the permanent collections in accordance with the Living Collections Policy [link].
Dana Greenhouse Production Staff
  • Produces the next generation of accessions destined for the permanent collections, as well as ensures the long-term survival of existing lineages through repropagation techniques, including cuttings and grafting.
  • Shares propagules with sister institutions and distributes plant material for research purposes.

Kathryn Richardson
  • 02/09/2018

In 2016, Alexander Susko led a project, Targets of Selection and Environmental Association in Rhododendron sect. Pentanthera, studying genetic variation that has been selected upon in naturally occurring Rhododendron sect. Pentanthera species and populations. This project includes two research objectives for ascertaining adaptive genetic variation in a group of woody species:
 

  1. Identify genetic targets of selection using transcriptome-wide polymorphism data across North American deciduous azalea species
 
  1. Associate transcriptome-wide polymorphism data that are unique to North American deciduous azalea species or groups of species with environmental factors.
 
http://arnoldia.arboretum.harvard.edu/pdf/articles/2016-74-2-towards-broader-adaptability-of-north-american-deciduous-azaleas.pdf
 

Kathryn Richardson
  • 02/09/2018

In 2015, Daniel Sullivan began his project, Establishing a collection of dried emerging leaf tissue as a resource for molecular studies of the living collections at the Arnold Arboretum, to establish a resource for future molecular studies. This project enhances the utility of its collections by creating a resource for current and future molecular studies.
 

  1. Appropriate accessions will be identified and flagged, and leaf tissue will be collected in the spring as the leaves are just emerging from the buds.
 
  1. Collected tissue will be dried in small packets over silica gel, five packets per accession, with appropriate information on each packet (Genus & species; accession number, date collected; tissue type; collector).

Kathryn Richardson
  • 02/09/2018

In 2012, Dov Sax, Jesse Bellemare, and Liz Ryan led a project, Using native, naturalized and horticultural ranges to characterize the realized, fundamental and tolerance niches, to characterize differences among the realized, fundamental and tolerance niche by comparing the climate conditions that species encounter in their native, naturalized and horticultural ranges. This project has three main components.
 

  1. Build species distribution models (SDMs) using climate records from county-level occurrences for over 600 native species that are naturalized in New England and California. We will contrast these native-based SDMs against conditions experienced in their naturalized ranges to estimate the frequency and magnitude of differences between realized and fundamental niches.
 
  1. Build a database of US-native plants sold at nurseries in mid-Atlantic and New England states. This will allow us to examine tolerance for conditions beyond those experienced in species realized distributions.
 
  1. Measure frost damage, growth and reproduction of US-natives grown beyond their native distributions in botanical gardens.

Kathryn Richardson
  • 02/09/2018

As part of its commitment to the Center for Plant Conservation (CPC), the Arnold Arboretum of Harvard University maintains and develops its collection of Rhododendron vaseyi.  Our primary goal is to preserve the highest level of intraspecific diversity as is practicable and provide access to researchers, educators, and the general public.
 
In 2018, our Rhododendron vaseyi collection includes: 26 accessions representing 26 distinct lineages, 4 plants growing in our nursery, and 41 plants growing outdoors in the living collections. Each plant within an accession is maintained individually, separated by provenance, and their placement in the landscape (10 distinct locations within the 281 acre landscape) ensures individual populations/genetics remain separate.
 

Nature Serve Biotics
  • 05/02/2017

A narrow endemic, Rhododendron vaseyi is rare and restricted to the Blue Ridge Mountains of North Carolina. Known from over thirty-five occurrences, the plant is threatened by development in the mountains, plant collecting, and the damming of mountain streams.

Irina Kadis
  • 01/01/2010

The main danger comes from irresponsible and uncontrolled development of vacation and retirement housing. Bog drainage results in total destruction of habitats. Amateur gardeners and nurserymen illegally collect plants from the wild.

Irina Kadis
  • 01/01/2010

Individual numbers are unknown.

Irina Kadis
  • 01/01/2010

Schreiber et al. (2000) conducted a genetic study of 15 currently recognized species in Rhododendron L. section Pentanthera G. Don. and found that they were all closely related.

Irina Kadis
  • 01/01/2010

There is no formal management plan.

Irina Kadis
  • 01/01/2010

Management needs include assessing and monitoring populations as well as devising a conservation plan that would offer protection for this plant.

Irina Kadis
  • 01/01/2010

One of the hardy American rhododendrons, very shade tolerant, also tolerant of soil compaction, poor drainage, and floods. It demands wet to moist growing conditions and strongly to moderately acid soil reaction (4.5-6.0). However, once established, pinkshell azalea can tolerate a wide variety of conditions and even survive droughts. Having been cultivated in the Arnold Arboretum since 1880, it proved to be hardy in Boston and is valued for cultivation all over the USA and in Europe. The flowers are frost resistant, so that it is successfully grown in Scandinavia. Cultivars: 'White find' is originating from a wild-collected form with white flowers. Another form with white flowers, f. album, was found among seedlings grown at the Arnold Arboretum and also at Kew Gardens and was used for the cultivar 'Album'. 'Suva' has pink flowers. Apparently, R. vaseyi does not hybridize and stays stable when grown from seed. Propagation from seed: sow into milled Sphagnum, maintain humidity under cover, water carefully. Seedlings are tiny and growing slowly. Put them a few per pot first, to reduce the risk of overwatering; repot once they achieve sufficient size. Propagation from softwood cuttings: take cuttings in May-June, keep them under fog or mist in 50/50 sand-perlite. With 2,500-5,000 ppm K-IBA or H # 3 treatment, the rooting rate is 70-80%. Cuttings become more secure once they survive through the first winter.

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Photos
Nomenclature
Taxon Rhododendron vaseyi
Authority Gray
Family Ericaceae
CPC Number 3739
ITIS 23730
USDA RHVA
Common Names pinkshell azalea | pink-shell Azalea
Associated Scientific Names Rhododendron vaseyi | Biltia vaseyi | Azalea vaseyi
Distribution Historically, this species was found only in six sites in the mountains of North Carolina (Radford et al. 1968). It is now known from the Blue Ridge from Ashe County south to Macon County, Transylvania Co. in western North Carolina. Type locality: Balsam Mountain near Webster (Jackson Co., western NC).
State Rank
State State Rank
Connecticut SNA
Massachusetts SNA
North Carolina S3
Habitat

R. vaseyi grows in mountain ravines, swamps, bogs, banks of streams, coniferous and oak forests at high elevations (3,000-5,500 ft) (Foote and Jones 1994). R. vaseyi appears to spread to clearings at places where the forest overstory has been logged. Therefore, logging does not constitute an immediate threat.It was once found in the wild in Massachusetts, near Halifax, where it appeared to be naturalized on the territory of an abandoned nursery in a swamp as well as on sandy soil. (Wilson and Rehder 1921).

Ecological Relationships

Ecological relationships are unknown.

Pollinators
Common Name Name in Text Association Type Source InteractionID

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