History of Rhododendron Discovery & Culture

• Discovery
• Explorers
  • Aberconway, Henry Duncan, 2nd Baron
  • Forrest, George
  • Fortune,  Robert
  • Fraser, John
  • Hooker, Sir Joseph D.
  • Ludlow, Frank
  • Ward, Frank Kingdon
  • Wilson, Ernest Henry
• Classification
• Genus Rhododendron Taxonomic Tree
• Native Rhododendron of North America
• First 50 Years of Hybrids and Hybridizers
• Index to Other Azalea & Rhodendron Pages 

Discovery

The first Rhododendron to be classified and named was R. hirsutum. It was discovered by the 16th century Flemish botanist, Charles l'Ecluse, who later became called Clusius. When it was introduced to Britain in 1656 from the European Alps, R. hirsutum (the Alpine Rose) was the first species of Rhododendron in cultivation.

As a historical reference, it should be noted that the Japanese were raising hybrids of R. indicum and R. tamurae in the 17th century. The Japanese book "A Brocade Pillow" which was published in 1692 carefully describes and classifies the color patterns of these plants which are called Satsuki Azaleas today.

Exploration in America came as a result of a partnership between English Quaker Peter Collinson and botanist/farmer John Bartram of Pennsylvania. This led to the importation to England of the American natives, R. canescens, R. nudiflorum, and R. viscosum in 1734, and R. maximum in 1736.

R. ferrugineum, another species from the European Alps also called the Alpine Rose, came along in 1752. The two plants called the Alpine Rose are perhaps the only rhododendron to do well in limestone soils. Claes Alstoemer discovered R. ponticum, a native of Armenia, which country was known to the ancients as Pontus, was found in Spain between Cadiz and Gibraltar around 1750 and it reached England in 1763. Some regions of the UK are overrun by this species.

In 1735, Karl von Linne (latinized Linnaeus), a Swedish naturalist, proposed the currently accepted binomial system of nomenclature to replace the cumbersome descriptive method that varied from one author to another, creating much confusion. Linnaeus used the term rhododendron in 1753 for only a few species: R. ponticum of Asia Minor, R. dauricum of Siberia, R. maximum from America, R. ferrugineum and R. hirsutum of the European Alps, and the circumpolar R. lapponicum. In Linnaeus' 'Supplement', R. chrysanthum was described. He listed Azalea as a separate genus, namely A. lutea (now R. indicum), and A. viscosa (later R. nudiflora and now R. viscosum). Linnaeus first described R. canadense, the Rhodora Azalea, in 1762. It is found from Eastern Quebec to Newfoundland and Nova Scotia, and south the northern parts of Pennsylvania and New Jersey.

The German naturalist Pallas described four rhododendron species native to eastern Europe and to Asia: R. dauricum in 1780, R. camtschaticum in 1784, R. flavum (which is now called R. luteum) in 1793, and R. chrysanthum in 1796.

Exact date of discovery for R. flammeum (also knows as R. speciosum) is not known, but plants of this species were first described by Aiton at Kew Gardens in 1789 and were probably sent there by William Bartram prior to that date.

R. macrophyllum, the Pacific Rhododendron, found in the North America from Northern California to British Columbia was discovered in 1792 by Archibald Menzies

R. carolinianum (the Carolina form of R. minus) was first collected by A. Michaux in 1792 and R. calendulaceum (the flame azalea) was first collected by A. Michaux in 1795 from the Blue Ridge Mountains of North Carolina.

By 1800 there were only twelve species known in cultivation. Gifts from the Russian collector, Count Pushkin, R. caucasicum arrived in England in 1803 and R. minus came from America in the first few years of the new century.

R. obtusum, known as a garden plant for centuries by the Japanese who called the shrub "Kirishima-tsutsuji", was mentioned in 1712 by Kaempfer, who used the Japanese name. It is a native of Japan but was introduced to England in 1844 by Robert Fortune from a Chinese garden. This 'wild' form, called R. obtusum f. japonicum by E. H. Wilson was considered by him to be the parent of all "Kurume Azaleas". This species was described as Azalea indica by Thunberg in 'Flowers of Japan' in 1784.

In 1809 R. catawbiense was introduced from North Carolina. It later became the principal source of hardiness in the garden hybrids which have graced our gardens for generations. It was collected by John Fraser and his son while collecting plants for Russian Emperor Paul. R. arborescens was first described by John Bartram in 1814.

The first of many Rhododendron which were to come from southeastern Asia was the tree species, R. arboreum, with blood-red flowers, which was discovered by Captain Hardwicke in 1799 and arrived from India in 1811. In 1821 Don introduced R. anthopogen and R. setosum from Asia. In 1823, R. molle, destined to become famous as one of the parents of the Mollis hybrids, was introduced from China. In 1832, R. zeylanicum (a subspecies of R. arboreum) came into England from Ceylon. From the Himalayan regions of Nepal and Sikkim, R. campanulatum was introduced in 1825 and the beautiful R. barbatum was introduced in 1849. R. scarbum was introduced by Don in 1834 from Japan.

R. mucronatum (variously described as Azalea rosmarinifolia, (Johannes) Burman (1768); Azalea mucronata (Carl Ludwig) Blume (1823); Azalea indica alba, Lindley (1824); Azalea ledifolia, Hooker (1829) and other names familiar to gardeners), was mentioned by Engelbert Kaempfer in 1712 under its Japanese name "Jedogawa-tsutsuji". According to John Lindley in 1824, this species was sent to Joseph Poole from China to Brookes Nursery at Ball's Pond in 1819.

R. japonicum (now known as a subspecies of R. degronianum) was known by other names and is often confused with the Chinese deciduous azalea species R. molle. It is native only to Japan where it is common over a great part of Hondo, the main island and elsewhere. Taken to Holland in 1830 by Philipp Franz von Siebold, it was used in hybridizing with R. molle to produce the "Mollis Azalea".

R. formosanum was introduced from India in 1832 by Wallich.

R. reticulatum, a native of much of Japan, was brought to England by Knight of Chelsea about 1832 to1833, but it may have been lost. Several later introductions were made.

In 1834, Sir William Jackson Hooker introduced R. albiflorum from the West Coast of the North America. In 1835, Siebold and Zuccarini introduced R. metternichii (now knows as R. degronianum ssp. degronianum) from Japan.

In 1849 and 1850 Sir Joseph Hooker's expedition to Sikkim in the eastern Himalayas discovered forty-five new species including the yellow-flowered R. campylocarpum and R. wightii; the red-flowered R. thomsonii; the small trees, R. falconeri, R. grande, and R. hodgsonii, with their enormous leaves; the epiphytes, R. dalhousiae and R. maddenii; the large vigorous R. griffithianum with massive white flowers; and the interesting R. triflorum, R. edgeworthii, R. fulgens, R. niveum, R. wallichii, R. lanatum, R. glaucophyllum, R. cinnabarinum, and R. lepidotum. Booth found R. hookeri and R. nuttalli in Bhutan in 1852. Planchon found R. simsii in 1854.

In 1855 Robert Fortune discovered R. ovatum in 1854 and R. fortunei in 1855 in Chekiang, China. It became the foundation of an important series of hybrids hardy in the United States as far north as Boston.

The next wave of exploration in 1881 was the outcome of earlier discoveries by French Catholic missionaries, Péres Armand David, Pere Jean-Marie Delavay and Paul Farges whose discovered were name R. davidii, R. delavayi, R. fargesii, and R. souliei. David also discovered R. calophytum. Delavay also discovered R. ciliicalyx, R. fictolacteum, R. lacteum, R. neriiflorum, and R. campylogynum in 1884; R. crassum and R. haematodes in 1885; R. bullatum, R. irroratum, and R. heliolepis in 1886; R. sulfureum in 1887; and R. racemosum, R. spinuliferum, R. rubiginosum and R. yunnanense in 1889; all in Yunnan, China. Farges also discovered R. adenopodum at 6,000 feet elevation in Szechuan/Hupeh, China. Rev. Souliei discovered R. chasmanthum and R. vernicosum in 1893, R. saluense in 1894, and R. wardii in 1895, in Yunnan, China. Rev. Ernest Faber discovered R. concinnum in Yunnan, China, in 1886. Many of these plants were grown from seed and introduced by Forrest.

In 1885 Baron Ungern-Sternberg discovered R. smirnowii and R. ungernii in the Caucasus Mountains.

The discoveries by the French missionaries led to a systematic search stated in 1899 and followed up in 1903-4 by Dr. Ernest Wilson for plants in China. Wilson found R. discolor, R. praevernum and R. ponticum in 1900; R. micranthum and R. sutchuenense in 1901; and R. ambiguum, R. intricatum, R. longesquamatum, R. obiculare, R. oreodoxa, R. tricanthum, R. wasonii, and R. davidsonianum in 1904 in Szechuan, China. Wilson introduced R. insigne R. williamsianum in 1908 and R. moupinense in 1909.

Wilson's work lead to a flood of expeditions by plant explorers to Asia. In 1904 George Forrest and Reginald Farrer explored Yunnan, China. Forrest discovered R. haemaleum and R. strigillosum in 1904; R. forrestii in 1905; R. oreotrephes in 1906; R. fulvum and R. sinogrande in 1912; R. puralbum, R. scintillans, and R. russatum in 1913; R. griersonianum and R. meddianum in 1917; R. keleticum and R. scyphocalyx in 1919; and R. taggianum in 1925. Forrest's and Farrer's work was carried on by Captain F. Kingdon-Ward in 1911, and Dr. Joseph F. Rock in 1920, the partners Ludlow and Sheriff and others. Kingdon-Ward discovered R. chryseum at 13,000 feet in Yunnan, China, in 1912; R. hippophaeoides at 12,000 feet in Yunnan, China, in 1913; R. megacalyx at 8,000 feet and R. calostrotum at 11,000 feet in Burma in 1914; R. leucaspis and R. valentinianum at 11,000 in Yunnan, China; R. pemakoense in Tibet in 1924 and R. recurvoides in July 1926 in the valley of the Di Chu in Upper Burma. Farrer and Kingdon-Ward discovered R. aperantum which was introduced by Forrest. Farrer discovered R. sperabile in Tibet in 1919. Forrest found and introduced R. stewartianum in Yunnan, China, in 1904; R. impeditum in Yunnan, China, in 1911; R. diaprepes in Yunnan, China, in 1913; R. eriogynum in Yunnan, China, in 1914; and R. didymum, R. eclecteum and R. eudoxum in Tibet in 1917. Farrer discovered R. caloxanthum in the Tibet/Yunnan region in 1919 and R. tephropeplum in Burma in 1920. From seed collected by Kingdon-Ward was identified two new species, R. concatenans and R. xanthocodon.

Meanwhile Dr. Augustine Henry, a medical officer, discovered R. augustinii in Szechuan, China, and R. racemosum was discovered by Delavay in Yunnan, China, in 1889. R. griersonianum and R. arizelum were discovered by George Forest in 1917 at about 10,000 feet elevation in Yunnan, China.

In 1937, R. aberconwayi was grown from seed from eastern Yunnan sent by Chinese assistants of George Forest to Lord Aberconway after Forest's death in 1932.

Most rhododendron species, over 900, are found in Southeast Asia, ranging from the Himalayas through Tibet, Burma, China, Thailand, Viet Nam, to Malaysia, Indonesia, Philippines and New Guinea. The distribution of native species extends down to northern Australia, up to Siberia, and around the world. Europe has 4 species, and in North America about 28 species are found.

A recent major discovery of a rhododendron is that of R. yakushimanum (aka. yakusimanum) first described by Japanese botanist T. Naki in 1920. Fortunately a Japanese botanist and nurseryman Dr. Wada sent two plants to Lionel de Rothschild's garden at Exbury in the south of England in 1932. Many forms of R. yakushimanum have been identified and most are considered to be subspecies of R. degronianum. Some are identified as subspecies of R. makinoi and R. keskei.

Other recent discoveries of new species include the giant yellow flowered R. sinofalconeri, the red species from the Yunnan/Sichuan border R. ochraceum, and the pink dwarf species R. dendrocharis. And more recently Kenneth Cox led an expedition to Tibet that discovered R. bulu and R. dignabile.

Two deciduous azalea species were recently discovered in Alabama (USA). R. eastmanii was discovered by Charles Eastman in 1980s and named in 1999. R. colemanii was discovered S. D. Coleman, Sr., in 1990s and named in 2008. Return to Top

Classification

Rhododendrons belong to the Ericaceae or heath family. Other members of the Ericaceae include the heaths (Erica), and heathers (Calluna), mountain laurel (Kalmia), lily-of-the-valley shrub (Pieris), cranberry (Vaccinium), Leucothe and Andromeda. Almost all of the heath family make good garden plants.

When Linnaeus created the botanical grouping called genus Rhododendron in 1753, he created a separate genus for Azaleas containing 6 species. In 1796 Salisbury pointed out that Azalea and Rhododendron could not be maintained as distinct genera. In 1834, George Don subdivided the genus Rhododendron into 8 sections which were recognized until 2004. Azaleas comprised two of these sections, Subgenus Pentanthera typified by Rhododendron nudiflorum and Subgenus Tsutsusi typified by Rhododendron Tsutsusi.

The extensive collections of Rhododendron in the early 1900's from southern Asia made by Forrest, Rock, Kingdom-Ward, and others stimulated taxonomic work at Edinburgh Botanic Garden and Herbarium under the direction of Bayley Balfour. The horticulturally based classification consists of about 45 series. The artificial classification was intended as a temporary measure, but it became firmly entrenched following the publication of The Species of Rhododendron in 1930 by the Royal Horticultural Society. This system was designed to cope with the vast quantities of new plant material received from the Orient, North America, etc. Balfour intended to revise the temporary system but died before it could be accomplished.

The Series system does not attempt to classify species under their subgenera and section as proposed in the International Rules of Botanical Nomenclature. Further, it is based largely on cultivated plants rather than Rhododendron found in the wild.

The Eight Subgenera prior to 2004

With many species discovered over several centuries the genus Rhododendron has been subdivided into groups and revised several times.. Up until 2004 the genus was divided into eight subgenera under the taxonomic system of Chamberlain et al. (1996):

1. Rhododendron (lepidotes)
2. Hymenanthes (elepidotes)
3. Pentanthera (deciduous azaleas)
4. Tsutsutsi (evergreen azaleas)
5. Azaleastrum (R. ovatum and R. stamineum)
6. Candidastrum (R. albiflorum)
7. Mumeazalea (R. semibarbatum)
8. Therorhodion (R. camtshaticum)

The first four of these subgenera contain all species the entire genus except for five. Of the last four Candidastrum, Mumeazalea and Therorhodion each include only one species (R. albiflorum, R. semibarbatum and R. camtshaticum respectively) while Azaleastrum includes two species (R. ovatum and R. stamineum).

Subgenera Rhododendron and Hymenanthes include the plants that gardeners recognize as the "true" rhododendrons. Some of these, the lepidote rhododendrons, have small scales on their leaves and make up the subgenera Rhododendron. Elepidote rhododendrons, those without leaf scales, form the subgenera Hymenanthes.

Subgenus Pentanthera covered the deciduous azaleas and Tsutsutsi covered the evergreen azaleas.

A list of all species and their classification is provided in the Genus Rhododendron Taxonomic Tree

The Five Subgenera proposed in 2004

Based upon genetic and chemical data, in 2004, Loretta Goetsch, Andrew Eckert and Benjamin Hall of the University of Washington proposed and in 2005 published a recommendation that the Genus Rhododendron be revised and subdivided into five subgenera:

1. Rhododendron (lepidotes)
2. Hymenanthes (elepidotes & deciduous azaleas)
3. Azaleastrum (evergreen azaleas)
4. Choniastrum (R. campionae, R. honcockii, R. latoucheae, R. moulmainense, R. stamineum)
5. Therorhodion (R. camtschaticum)

Some of the subgenera are divided into sections, which are further divided into subsections. There are also groupings known as alliances and aggregates composed of very closely related species.

For taxa outside of subgenus Rhododendron, this system eliminates three subgenera and two sections that are present in the 1996 taxonomic system of Chamberlain et al.

Section Pentanthera is included within subgenus Hymenanthes.

Sections Sciadorhodion and Viscidula and R. vaseyi (section Rhodora) from the discontinued subgenus Pentanthera are combined with sections Azaleastrum, Tsutsusi and Brachycalyx to form an expanded and revised subgenus Azaleastrum. Sister groups in this subgenus are the sections Tsutsusi (largely evergreen) and Sciadorhodion (entirely deciduous)

Since Choniastrum lacks lepidote scales on the leaves, Goetsch et al. propose that Choniastrum be considered a separate subgenus.

A list of all species and their proposed classification is provided in the Proposed Genus Rhododendron Taxonomic Tree. This chart assumes subsections and alliances are carried over from the old Taxonomic Tree. This is probably not a safe assumption but is a pragmatic one since I don't have the faintest idea what is being considered.

If you understand the basic ideas of genus, subgenus, section and species you will have a better understanding of rhododendron naming conventions. A rhododendron species can be uniquely identified with the genus and species. Hence Rhododendron albiflorum defines a unique species. There may be another genus that uses the name albiflorum since it is Latin for "white flowering". Return to Top

Common Native Rhododendrons and Azaleas of North America

According to the USDA native stands of species of rhododendrons are found in all US states and provences of Canada except:

There are at least 27 species that are native to North America.

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R. alabamense, the Alabama Azalea, is a deciduous azalea found in Alabama and adjacent states. It has snowy white flowers with a prominent yellow blotch. Blooming in midseason, the flowers have a distinct lemon-spice fragrance and measure .8 to 1.5 inches across. Originally thought to be a white form of R. periclymenoides (R. nudiflorum) , this plant was first described by Dr. C. Mohr in 1883. It grows naturally in north central Alabama, and western to central Georgia and South Carolina. R. alabamense is low to medium in height, and spreads by underground stems or stolons. It propagates with relative ease from soft wood cuttings and makes a delightful landscape plant. [back to table]

R. albiflorum, the Cascade Azalea, is an upright, white-flowering, deciduous rhododendron that is found in western North America from British Columbia and Alberta to Oregon and Colorado near the timberline. Rhododendron albiflorum was discovered by Mr. Drummond during the early nineteenth century. In 1834, Sir William Jackson Hooker sent seeds to Dr. Graham of Edinburgh, where it flowered in Scotland in 1837. John G. Millais reported having seen thousands of acres of it growing above 4,000 feet elevation in the mountains of Washington State and British Columbia in such dense thickets as to be called "The Miner's Curse." It does not do well in cultivation except in Scotland. [back to table]

R. arborescens, the Sweet or Smooth Azalea, is a deciduous azalea found from Pennsylvania south to Georgia and Alabama. It is a good late flowering, scented species that can be used in cultivation. The flowers have a strong, cinnamon-like fragrance. It has white to blush pink flowers with red stamens, and a very strong fragrance similar to heliotrope. It blooms in late spring to early summer and individual flowers measure 1.5 to 2 inches across. It has glossy leaves and red fall foliage. Rhododendron arborescens was probably discovered by John or William Bartram and appeared in Bartram's catalogue as Azalea arborea. It may have been sent to England by the Bartrams before the introduction date of 1818 stated by Robert Sweet. Pursh referred to it as the finest ornamental shrub he knew in 1814 after seeing it in the Bartram garden. Ernest Henry Wilson stated this handsome plant was still very seldom seen in cultivation in 1921. This species has a wide distribution in the eastern United States, but can usually be found growing near streams or moist areas. It is sometimes known as the "Smooth Azalea" because the stems are very smooth and do not have hairs similar to the other azaleas. An excellent landscape plant, R. arborescens can perfume a wide area when in bloom. Relatively easy to propagate, there are a number of excellent forms in the trade. [back to table]

R. atlanticum, the Atlantic or Dwarf or Coastal Azalea, is a low deciduous azalea found on coastal plains from Pennsylvania and Delaware south to Georgia. It is a good late flowering, scented species that can be used in cultivation. Flowers have a rose-like fragrance. It is a common understory plant along the south eastern coastal plains of the United States. The white flowers are 1 to 1.5 inches across, but are often blushed with pink on the outside and some have a yellow blotch. Collected by John Clayton in 1743, this plant was appreciated more in England than in its native land. The plant habit is relatively low, 3 to 5 feet tall, but stoloniferous. Spreading by underground stems, R. atlanticum can develop into very large colonies of an acre or more in sandy soils. R. atlanticum is easy to propagate, and makes a nice landscape plant in heavier soils which will restrict the spreading habit. [back to table]

R. austrinum, the Florida Azalea, is a deciduous azalea found from northwest Florida to Georgia, Alabama and southeast Mississippi. This plant blooms in early spring as the leaves are beginning to expand. The fragrant, sometimes lemony, blossoms come in shades of orange through gold and yellow with a reddish tube, and measure approximately 1 to 1.5 inches across. This species has very long stamens and the tube of the flower is often flushed with red but there is no blotch. Discovered by Dr. A. W. Chapman before 1865, R. austrinum is similar in many respects to R. canescens including the sticky glanular hairs on the flower tube, but differs in the color variations which are orange to yellow rather than pink to white. R. austrinum makes an excellent landscape plant as well as a valuable hybridizing resource, especially in southern gardens where heat tolerance is important. [back to table]

R. calendulaceum, the Flame Azalea, is a tall deciduous azalea found from southwest Pennsylvania south through the Appalachian Mountains to Georgia and Alabama and west to West Virginia and southeastern Ohio. It is surely one of the most spectacular native shrubs of the Appalachian Mountains. The flowers are larger than most of the natives, measuring from 1.5 to 2.5 inches across, and come in a wide range of colors from brilliant shades of yellow to orange or red, with a large prominent yellow to orange blotch on the upper lobe (petal). R. calendulaceum, described as Azalea lutea by Linnaeus in 1753 and changed by him to A. nudiflora in 1762, was discovered in Northern Georgia in 1774 by William Bartram who described the species as Azalea flammea in 'Travels' (1790). There were numerous introductions from America to Europe where the species was highly prized. This species is difficult to propagate by cuttings, but is easily raised from seed. R. calendulaceum is a naturally occurring tetraploid, having twice the number of chromosomes in comparison to the other native species. Because of this fact, it does not hybridize easily with most of the other natives and even if a first generation cross is made, the resulting hybrids are often sterile. [back to table]

R. camtschaticum formerly called Therorhodion camtschaticum is an deciduous elepidote rhododendron found in northeast Asia to Japan, coastal Alaska, British Columbia and also abundant in West Greenland, . This low growing rhododendron has the unusual trait that the one to three flowers appear at the end of young leafy shoots of the current year, and not from special buds. It does well in cultivation in alpine regions of Northern Germany and Eastern Scotland. It is difficult to grow in warmer climates. R. camtschaticum was first described in 1784 by Pallas. R. camtschaticum was first introduced to Britain in 1799. It was rare in British gardens in 1917 due to problems of cultivation.[back to table]

R. canadense, the Rhodora Azalea, is a low deciduous azalea found from Eastern Quebec to Newfoundland and Nova Scotia, and south the northern parts of Pennsylvania and New Jersey. It has showy lavender flowers. It has a white form that comes true from seed. It does well in moist acidic soils. Rhododendron canadense is a very unusual native azalea species and was originally considered an entirely separate genus, Rhodora . The top three petals of the flower are fused together almost to the end to form a single lobe, whereas the bottom two are completely separate lips. The purplish pink blossoms are approximately 1.5 inches across and have 10 stamens, twice the number of most east coast natives. R. canadense was first described and pictured by Henri Louis Duhamel du Monceau in the 'Botanic Garden' in Paris in March 1756, where it had been brought from Canada and later by Linnaeus in 1762. Samuel Gottlieb Gmelin referred it to the genus Rhododendron in 1791, and that same year the species was introduced to England. R. canadense is a low stoloniferous shrub that is the most northern of the east coast native azaleas, the species is very cold hardy but a difficult plant where summers are hot and dry.

R. canescens, the Florida Pinxter or Piedmont Azalea, has white to pinkish tubular flowers with stamens two to three times longer than the petals. It is often confused with R. periclymenoides. Both are medium deciduous azaleas that are found in the Carolinas but can be separated by the flower tubes, which in R. periclymenoidesare fuzzy. R. canescens also has tiny hairs, but they are sticky and glandular. Another noticeable difference is that when a flower of R. periclymenoides dies, a ridge on the corolla tube tends to catch on the end of the pistil so that a flower cluster past its prime consists of several dangling blossoms. Although widespread in the eastern half of the U.S., these two wild azaleas differ in distribution. In South Carolina, for example, R. periclymenoides is a Piedmont plant, with almost no specimens reported from the Sandhills or Coastal plain, while R. canescens is predominantly a Low Country plant absent from the Piedmont, except in counties that border the Savannah River. In general, if it grows wild north of South Carolina, it's likely R. periclymenoides; south of the Palmetto State and it's probably R. canescens. Both species prefer moist, humus-laden, acidic soil but seem to do equally well in shade or sun. Old specimens can reach heights of 12-15 feet and have multiple stems or trunks up to 5" in diameter. Rhododendron canescens was discovered by Mark Catesby, who published a picture of it in 1731. Michaux collected it in South Carolina between 1784 and 1796. It was probably introduced to England in the mid-eighteenth century. [back to table]

R. catawbiense, the Mountain Rosebay, is a medium to tall elepidote rhododendron native from Virginia south to Georgia and west to Alabama, Kentucky and West Virginia. It is quite hardy and has a good plant habit. It has large rose to purple-lilac colored flowers. It was first collected by A. Michaux in 1803 and was introduced to Britain by John Fraser in 1809. Through selection and hybridization this species was parent to a very valuable group of May flowering garden rhododendrons from the white R. 'Catawbiense Album' to the violet R. 'Catawbiense Boursault' including 'Everestianum' and 'Fastuosum Floro Plenum'.. [back to table]

R. colemanii, the Red Hills azalea, from the upper Coastal Plain of Alabama and Western Georgia, was named in 2008. It was initially collected and propagated by S. D. Coleman, Sr. It is one of the tallest, most fragrant and most richly colored of all the native azaleas. Different plants may show flower colors ranging from pure white to deep pink, and even yellow or nearly orange. It's also late-blooming, typically flowering in early May. In the field, the azalea can be distinguished from R. alabamense and other coastal azaleas by its late spring (early to mid May) flowering time, its wide range of flower color (white, pink or yellow), longer flower buds, its often warty seed capsules with glandular hairs, and its taller stature (3-7 m). Its natural distribution extends from southwestern Alabama to the Chattahoochee Valley in Georgia. [back to table]

R. cumberlandense, the Cumberland Azalea, formerly R. bakeri, is a low deciduous azalea found in Kentucky, Virginia, Tennessee, North Carolina, Georgia and Alabama. It is an excellent, low-growing, late blooming orange to red-flowered azalea suitable for small gardens. Plant height varies from 1 foot up to 6 feet. The flowers are not large, about 1.5 to 1.75 inches across, and typically range from yellowish-orange to deep red. This species is sometimes difficult to distinguish from the larger flowered R. calendulaceum , but the blossoms generally appear several weeks later after the leaves have fully expanded and the undersides of the leaves are usually waxy white or bluish in color. The species distinction for R. cumberlandense was first described by Lemon and McKay in 1937. This native azalea makes an excellent landscape plant in its own right, but it also hybridizes easily with many of the other species, producing beautiful hybrids in a broad range of colors. [back to table]

R. eastmanii, the May white azalea, is a deciduous azalea found in South Carolina in 13 counties of the piedmont and coastal plain to date, officially named, described and proposed as a new species in Novon in September of 1999. It has snowy white flowers with a prominent yellow blotch. Blooming in mid May, the flowers have a distinct, strong, fresh fragrance and measure .8 to 1.5 inches across. Originally thought to be R. alabamense, this plant was first described, noticed and thought to be different from known S.C. species by Charles Eastman in the early 1980s, one hundred years after Dr. C. Mohr discovered R. alabamense. R. eastmanii is low to medium in height, and has a clump habit but does not spread by underground stems. It propagates with relative ease from woody cuttings and makes a delightful landscape plant. [back to table]

R. flammeum, the Oconee Azalea, formerly R. speciosum, is a deciduous azalea found in the lower Piedmont from central Georgia to South Carolina. It is seldom cultivated in cooler climates but does well in the southeast. Its blossoms are approximately 1.2 to 1.8 inches across and come is shades of yellow, yellow-orange or red. This species can be distinguished from the earlier blooming R. austrinum in that the flowers usually have a large yellow blotch on the top lobe (petal), they are not fragrant, nor do they have sticky glandular hairs on the corolla tube. R. speciosum was collected by Michaux on April 26 and 27, 1787 near Two Sisters Ferry on the Savannah River described in his 'Flora' as A. callendulacea v. flammea. Several other early collections were also made of this species. Sweet assigned the name R. speciosum in 1830. Plants of this species were described by Aiton at Kew Gardens in 1789 and were probably sent there by William Bartram prior to that date. This species is a heat tolerant shrub and holds much breeding potential where hot summer stress is a problem. [back to table]

R. groenlandicum, Labrador Tea, is an upright lepidote rhododendron that is found from the northern USA, through Canada and into Greenland. It blooms heavily with white trusses. It was introduced in 1763. [back to table]

R. lapponicum, the Lapland Rosebay, is a very low lepidote rhododendron found from Maine to Wisconsin and north from Quebec to Newfoundland. It has clusters of pink to lavender flowers. It is found on mountain tops and in sub arctic areas. It was first described by Wahlenberg in 1812. [back to table]

R. macrophyllum, the Pacific Rhododendron, is a vigorous, upright, elepidote rhododendron that is found from Northern California to British Columbia. Discovered in 1792 by Archibald Menzies, it has pink to rose colored flowers. It is seldom found in cultivation. It is related to Ponticum and Catawbiense. [back to table]

R. maximum, the Great Laurel, is a large elepidote rhododendron found from Nova Scotia to Georgia and west to Alabama and Ohio in dense forests. Since deer were introduced in Nova Scotia around 1887, R. maximum has apparently disappeared from Nova Scotia according to John Weagle of Halifax. This tall straggly plant has pinkish-white flowers. It long slightly narrow leaves have a thin indumentum on the underside. It is a large hardy plant with small trusses. R. maximum was introduced to England in 1736 by Peter Collinson from eastern North America, but as such was never very popular there. The true species was reported to be at Leonardslee by J. G. Millais in 1917. This species was one of the chief progenitors of a hardy group of English garden hybrids. [back to table]

R. minus, Carolina rhododendron, is a low growing lepidote rhododendron found from Florida and Alabama up to Tennessee and North Carolina in mountains and plains. R. minus, first described as such by Michaux in 1792, was long known as R. punctatum. John Fraser introduced the species to England in 1786 where it was still rare in 1917. R. minus was crossed with R. ferrugineum to give the curious shrub known as 'Daphnoides'. R. minus, is actually a composite of three distinct plants:

• R. minus var minus grows on the exposed cliffs of mountains, in the piedmont, and along streams of North and South Carolina, Georgia and Alabama. It is typically a straggly tall shrub but good horticultural selections for habit, late bloom time and color have been made.
  • The form growing in the Chattahoochee region of Georgia and Alabama is distinct horticulturally and more attractive in flower than the type from North Carolina. It is shorter and earlier blooming by two weeks than those from North Carolina. Flowers of the Chattahoochee R. minus often have yellow-orange flares.
  • The carolinia form is later blooming by two weeks. This form is very heat tolerant and has been used as a parent for very hardy hybrids such as P.J.M. It historically was called R. carolinianum. It is 3 to 6 feet high with a naturally rounded shape and dark green leaves 3 inches long. In mid-spring it is covered with 3-inch clusters of rose-pink flowers. The Carolina rhododendron is hardy to Zone 5, -15° F. This is one of the most satisfactory species for northern gardens, becoming a thickly branched, rounded shrub that usually grows 3 to 4 feet tall in 10 years. In mid-spring it is smothered with 3-inch clusters of small rosy pink flowers. The 1 1/2- to 3-inch dark green leaves are brown underneath. There is also a variety with pure white flowers and lighter green leaves. It was first collected by A. Michaux in 1792.The Carolinianum Group has openly funnel-shaped flowers with green flares, a shorter floral tube, and ovate leaves. It is a bushy and compact shrub, and not as leggy as it's siblings.
• R. minus, var chapmanii is an endangered variety often given species status as R. chapmanii. There are only 3 known populations in the hot coastal plains of northern Florida. Geographically isolated from R. minus var. minus it grows on sands that have abundant organic matter and are well drained at the surface but with permanently saturated acid water just below the surface. It prefers light shade and can be found between the drier pine-turkey oak vegetation and the moister titi (Cliftonia) bogs. R. minus var. chapmanii grows to 6 feet (2 m) tall, and is stoloniferous, resprouting easily when cut back. The leaves are smaller than var. minus, with a rounded leaf tip and more oval shape. The leaves are aromatic when crushed and the upper surface is distinctly rugose. There are reports of some variability in color forms in the wild. Breeding with R. minus var. chapmanii is thought to increase the heat tolerance of its offspring. [back to table]

R. neoglandulosum, Trapper's Tea or Glandular Labrador Tea, is an upright lepidote rhododendron that is found in the northwestern USA. It blooms heavily with white trusses. It was first introduced in 1894. It was long grown as Ledum glandulosum. [back to table]

R occidentale, the Pacific or Western Azalea, is a tall deciduous azalea found in the Pacific Coast states. The flower color is usually white or pale pink with a strong yellow flare, but my be red, yellow or orange-pink and occasionally the flare is maroon. The foliage turns red and copper shades in the fall. It is among the showiest of all species with bright colors on impressive flowers. However it is difficult to propagate and grow. It is considered impossible to grow on the East Coast. Rhododendron occidentale is the only native azalea that grows naturally west of the Rocky Mountains in the United States. William Lobb, a collector for Veitch and Sons of Exeter, is credited with having introduced R. occidentale to England in 1850. [back to table]

R. periclymenoides, formerly R. nudiflorum, the Pinxterbloom Azalea, is a medium deciduous azalea found widespread from Vermont and Massachusetts south to South Carolina and north Georgia and Alabama and west to Tennessee and Ohio. It has showy flowers that are either white, pale pink or deep pink. Pinxter-flower, with lightly fragrant inch-wide blooms, is perhaps the most common and most familiar wild azalea in the eastern U.S. The name "pinxter" comes not from its coloration but from the Dutch words Pinxter blomachee, which relate to the fact that this is supposedly the azalea that blossoms on Pentecost, 50 days past Easter. We suspect this name was given by folks in northern parts of the plant's range, since in the Carolinas it is more likely to be in bloom for Easter Sunday itself. R. periclymenoides, was probably discovered by John Banister. Plunkenet described it as "Cistus virginiana pericyclemeni flore ampliori et minus odorato". It was introduced to England between 1725 and 1730 by Peter Collinson who received it from John Bartram in America. [back to table]

R. prinophyllum, formerly R. roseum, is a medium deciduous azalea found from southwestern Quebec, through New England, to Appalachian Mountains in Oklahoma and Arkansas at the higher elevations. The flowers are typically rose pink measuring 1.2 to 1.8 inches across and are very fragrant. Assumed to be a form of R. periclymenoides (R. nudiflorum) since its first mention in 1787, it was first described as a distinct species in 1914 by Small but had been under cultivation as A. rosea in Europe before 1812. R. prinophyllum can be distinguished from R. periclymenoides by a number of characteristics including the fact that it is usually deeper pink in color and with a strong cinnamon to clove fragrance. R. prinophyllum is a good landscape plant for northeastern gardens, but may be more difficult in the south because of summer heat. [back to table]

R prunifolium, the Plumleaf Azalea, is a medium deciduous azalea found on the Georgia-Alabama border. The color ranges from orange-red to red, and occasionally orange or yellow. The petals have a deep red blotch. This species blooms very late, usually in late June or in July. Plants are usually 5 to 8 feet tall, although some mature plants may attain a height of 20 feet. First collected by R.M. Harper in 1913, R. prunifolium prefers more shade than most deciduous azaleas to prolong the flowers during hot summer months. It is the signature plant of Callaway Gardens in Pine Mountain, Georgia. [back to table]

R. subarticum, formerly Ledum subarticum, is an upright lepidote rhododendron that is found in the arctic regions of North America, Europe and Asia. It blooms heavily with white trusses. It does well in alpine gardens. [back to table]

R. vaseyi, the Pink Shell Azalea, is a medium to tall deciduous azalea found in North and South Carolina. It does very well in cultivation, especially in moist soils. It has showy dark pink flowers. It also has a white variation. It has showy fall foliage when the willow-like leaves turn yellow and red. Discovered by George Vasey in 1878, this native azalea has a relatively restricted natural habitat in four mountainous counties of North Carolina. Growing at elevations of 3000 to 5500 feet, the rare Pinkshell azalea can be seen in bloom along the Blue Ridge Parkway in early spring. [back to table]

R. viscosum, Swamp Honeysuckle, is a medium deciduous azalea found in low areas along stream banks from Maine to Georgia and west to Texas. Rhododendron viscosum now includes two closely related forms that were previously considered separate species, R. serrulatum and R. oblongifolium . The fragrant flowers with a clover-like fragrance are generally white to pale pink, and bloom after the leaves have fully expanded. Flowers vary in size from 0.75 to 1.5 inches across depending upon the form, but have a long narrow tube covered with sticky glandular hairs. The species has a wide distribution from Maine to Florida, and westward to Texas. R. viscosum was the first North American azalea grown in England. It can be distinguished from the other late blooming white, R. arborescens in that the stamens are greenish white rather than red, and the stems are not smooth but contain hairs. R. viscosum is a variable species closely related to R. serrulatum, R. abnorescens, R. oblongifolium, and R. atlanticum. These species are sometimes not easily distinguished from each other and have been frequently confused. Bishop Henry Compton raised the plant in 1680 from seed collected by John Bannister, an English missionary in eastern North America. John Banister sent a drawing of R. viscosum to Dr. Henry Compton, Bishop of London. Leonard Plundent published it in 'Phytographia' in 1692 after Banister's untimely death. The species was an important parent in early hybridizing efforts with deciduous azaleas. In1734, John Bartram, an American farmer-horticulturist, sent R. viscosum to Peter Collinson in England. [back to table]

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