In the Greek, rhododendron means ‘rose tree’. However, these trees and shrubs are not at all related to roses, but belong to the heath family (Ericaceae). From a distance, though, the flower clusters of certain species do resemble roses.
It seems that to the ancient Greeks, the flowers clusters of certain rhododendron species resembled roses. One of these could have been R. barbatum, here photographed near Tharepati, Langtang National Park, central Nepal. (Photo copyright © by Kaj Halberg)
The genus Rhododendron is huge, comprising c. 1,025 species worldwide, found mainly in temperate and subtropical areas of Eurasia, North America, Tropical Asia, and New Guinea, with the largest concentrations encountered in south-western China, the Himalaya, the Greater Sunda Islands, and New Guinea. A few species are found in Arctic regions, and a few others in areas with a genuine tropical climate, including one species in Queensland, Australia.
Rhododendrons vary greatly in size, from dwarf shrubs like R. pumilum, R. nivale, and R. lapponicum, which are usually less than 20 centimetres high, to Himalayan species like R. arboreum and R. grande, which can grow to 15 metres tall.
Rhododendron pumilum rarely grows taller than 10 centimetres. The habitat of this dwarf shrub, which is distributed from eastern Nepal eastwards to south-western China, is open slopes and rocks. (Photo copyright © by Kaj Halberg)
Rhododendron arboreum, a widespread Asian species, can grow to 15 metres tall. (Photo copyright © by Kaj Halberg)
The flowers of most rhododendron species are various shades of red, pink, or lilac, while other colours include white, yellow, and greenish.
In the Himalaya, the intensity of the red colour of Rhododendron arboreum flowers decreases with higher altitude, and near the upper limit of its distribution, you sometimes encounter trees with white flowers. This species is the national plant of Nepal, called lali guras (lal means ‘red’).
These pictures show three shades of flower colour in Rhododendron arboreum. (Photos copyright © by Kaj Halberg)
Flowers of Rhododendron lepidotum come in three colour forms. This dwarf shrub is one of the most widespread Himalayan species, found from northern Pakistan eastwards to south-western China.
The commonest flower colour in Rhododendron lepidotum is red, and white is also widespread, while the yellow-flowered form, seen in the lower picture, is rare. (Photos copyright © by Kaj Halberg)
Rhododendron setosum is another dwarf shrub, distributed from western Nepal eastwards to south-western China. Its funnel-shaped flowers are reddish-violet, while a variety with pink flowers is sometimes seen.
Rhododendron setosum, photographed in the Khumbu region, eastern Nepal. In the upper picture, the peak of Taboche (6367 m) is seen in the background. The lower picture shows the pink-flowered form, next to flowers of a normal colour. (Photos copyright © by Kaj Halberg)
The inflorescence of most rhododendron species is an umbel-like cluster, the corolla being funnel- or bell-shaped, with five lobes.
This inflorescence of Rhododendron arboreum, seen in Helambu, Nepal, is still unfolded. (Photo copyright © by Kaj Halberg)
Flowers of the Himalayan species Rhododendron campylocarpum are bell-shaped. (Photo copyright © by Kaj Halberg)
The fruit is a capsule, containing between four and twenty chambers. In the pictures below, fruits from the previous year are still sitting on the plant.
Fruit cluster of Rhododendron arboreum, Helambu, Nepal. (Photo copyright © by Kaj Halberg)
Fruit cluster of Pacific rhododendron (Rhododendron macrophyllum), Redwood National Park, California. (Photo copyright © by Kaj Halberg)
Many rhododendron species are very tough, growing under severe climatic conditions. Five such species are shown below.
Rhododendron arboreum (top) and R. campanulatum, both photographed in Langtang National Park, central Nepal. (Photos copyright © by Kaj Halberg)
Subspecies parviflorum of Lapland rhododendron (Rhododendron lapponicum) is found in eastern Siberia, where temperatures in winter can drop to below -30o Centigrade. (Photo copyright © by Kaj Halberg)
Early in the morning, the flowers of this hardy Rhododendron fulgens are covered in rime. This species grows at high altitudes in the Himalaya, from eastern Nepal to south-eastern Tibet. – Barun Valley, eastern Nepal. (Photo copyright © by Kaj Halberg)
Flowers and leaves of this unidentified species in the Wumeng Shan Mountains, Guizhou Province, China, are covered in rime. (Photo copyright © by Kaj Halberg)
The name Rhododendron is used for evergreen as well as deciduous species, the latter often called azalea. European species are usually called by their German name, Alpenrose.
Yellow azalea (Rhododendron luteum) is found from Poland south through Austria and the Balkans, and thence eastwards to the Caucasus. Its sweet-smelling flowers attract bees, but the honey produced from them is actually toxic, and reports of people being poisoned by consuming this honey date as far back as to Classical Greece.
Yellow azalea, photographed on the Turkish Black Sea coast, near the town of Tirebolu. (Photo copyright © by Kaj Halberg)
Western azalea (Rhododendron occidentale) grows in coastal ranges of western North America, from Oregon south to the Mexican border. It is not known to occur east of the Cascade and Sierra Nevada Mountains.
Western azalea, Cave Junction, Oregon. (Photo copyright © by Kaj Halberg)
China is the absolute stronghold of the rhododendron genus, with no less than c. 571 species, of which 409 are endemic.
Rhododendron delavayi is a gorgeous species, distributed in south-western China, south-eastern Tibet, Bhutan, Arunachal Pradesh, and mountains of northern Myanmar, Thailand, and Vietnam.
Rhododendron delavayi, Wumeng Shan Mountains, Guizhou Province. (Photo copyright © by Kaj Halberg)
Rhododendron simsii (top) and an unidentified species, both from the Guizhou Province. (Photos copyright © by Kaj Halberg)
Flowers of the majorority of the 30 Taiwanese rhododendron species display white, pinkish, or violet colours, but those of Rhododendron oldhamii are a warm red. This species is found almost down to sea level, while most of the other species grow at high altitudes in the central part of the country.
Rhododendron oldhamii, photographed near Nanren Lake, Kenting National Park. (Photo copyright © by Kaj Halberg)
Rhododendron pseudochrysanthum is a gorgeous shrub, found at very high altitudes in the mountains of Taiwan, between 3,100 and 3,900 metres. Its flowers are white or pink.
Rhododendron pseudochrysanthum is common in the Hohuan Shan Mountains, where these pictures were taken. (Photos copyright © by Kaj Halberg)
As its name implies, the red-hairy azalea (Rhododendron rubropilosum) can be identified by the reddish-brown, glandular hairs on its twigs and leaves. This species is found in central Taiwan, at altitudes between 1,800 and 3,300 metres, often forming large thickets at higher altitudes.
Rhododendron rubropilosum, Hohuan Shan. (Photos copyright © by Kaj Halberg)
Formerly, Rhododendron morii, of central and eastern Taiwan, was regarded as a subspecies of R. pseudochrysanthum. Its flower colour comes in all shades between snow-white and pale pink.
The white-flowered form of Rhododendron morii, Hohuan Shan. (Photos copyright © by Kaj Halberg)
Pinkish form of Rhododendron morii, photographed on a foggy day in montane forest, Taipingshan National Forest. (Photos copyright © by Kaj Halberg)
The Himalaya is home to c. 100 species of rhododendron, the vast majority growing in the eastern part of the mountain chain. A tiny country like Bhutan, for instance, harbours more than 60 species. The further west you travel in the Himalaya, the fewer species you encounter. Eastern Nepal is home to c. 30 species, western Nepal to seven, and Pakistan to only four. The genus occurs in almost all vegetation zones, from subtropical to alpine, the major part found between 2,000 and 4,000 metres altitude.
Rhododendron arboreum is the tallest rhododendron species in the Himalaya, growing to 15 m. It is very common, and in March-April, when it is flowering, it adds a reddish or pinkish tinge to the forest in numerous places, stemming from millions of flowers. The intensity of the red flower colour decreases with altitude, and near the upper limit of its distribution, around 3,800 metres, you sometimes encounter trees with white flowers.
In the Annapurna area, central Nepal, where these pictures were taken, Rhododendron arboreum, when flowering, adds a reddish or pinkish tinge to the large tracts of forest. (Photos copyright © by Kaj Halberg)
In spring, the flowers of Rhododendron arboreum produce a profusion of pollen. For this reason, they are much visited by various bird species, in this picture a striated laughing-thrush (Garrulax striatus). – Annapurna, central Nepal. (Photo copyright © by Kaj Halberg)
In its widest sense, this species has an extensive distribution in Asia, from Pakistan eastwards to montane areas of northern Thailand and Vietnam, and with isolated populations in mountains of South India and Sri Lanka. The subspecies in South India is called Nilgiri rhododendron (R. arboreum ssp. nilagiricum), whereas the Sri Lanka rhododendron (R. arboreum ssp. zeylanicum) is sometimes regarded as a separate species, R. zeylanicum.
This picture shows Nilgiri rhododendron (R. arboreum ssp. nilagiricum), photographed in the Nilgiri Mountains, Tamil Nadu. (Photo copyright © by Kaj Halberg)
From a distance, Rhododendron barbatum is quite similar to R. arboreum, but a closer look reveals distinctive glandular bristles on its twigs and leaf-stalk, and its bark peels off in thin, cinnamon-coloured flakes. This species is very common in the Himalaya, found from Uttarakhand eastwards to Bhutan.
Rhododendron barbatum often forms pure stands at altitudes between 2,400 and 3,600 metres, as in this picture from Kutumsang, Langtang National Park, central Nepal. (Photo copyright © by Kaj Halberg)
This picture from Ghorepani, Annapurna, central Nepal, shows the distinctive bristles on a twig of Rhododendron barbatum. (Photo copyright © by Kaj Halberg)
The bark of Rhododendron barbatum peels off in thin, cinnamon-coloured flakes. (Photo copyright © by Kaj Halberg)
As its popular and specific names imply, the bell rhododendron (Rhododendron campanulatum) has bell-shaped flowers. This attractive shrub is very common in the Himalaya, forming dense thickets at altitudes between 2,800 and 4,000 metres.
Rhododendron campanulatum, Ghunsa Valley, eastern Nepal. (Photos copyright © by Kaj Halberg)
One of the characteristics of bell rhododendron is the rusty-coloured layer of hairs on the underside of its leaves. (Photo copyright © by Kaj Halberg)
Formerly, Rhododendron wallichii was regarded as a variety of R. campanulatum, but generally its flowers are paler, and the underside of its leaves is not hairy. The specific name was given in honour of Danish physician and botanist Nathaniel Wallich (1786-1854), who studied the Indian and Himalayan flora in the early 1800s.
This picture of Rhododendron wallichii is from the Khumbu area, eastern Nepal, where this species is very common. (Photo copyright © by Kaj Halberg)
The flowers of Rhododendron triflorum are a very pale yellow with a greenish tinge, sitting in clusters of three, as indicated by its specific name. Its bark peels off in thin, cinnamon-coloured flakes.
Rhododendron triflorum, Ghunsa Valley, eastern Nepal. (Photo copyright © by Kaj Halberg)
The large Rhododendron hodgsonii, which grows to 7 metres tall, is easily identified by its dense inflorescences and large leaves. The flower colour varies from whitish to deep pink. This species has a rather limited distribution, from eastern Nepal eastwards to south-eastern Tibet.
My guide Saila Tamang, standing in a dense growth of Rhododendron hodgsonii, Barun Valley, eastern Nepal. (Photo copyright © by Kaj Halberg)
Rhododendron hodgsonii, Ghunsa Valley, eastern Nepal. (Photos copyright © by Kaj Halberg)
Rhododendron campylocarpum is very common from eastern Nepal east to south-western China, at altitudes between 3,000 and 4,000 metres. In places, it brightens large tracts of forest with its beautiful, pale-yellow inflorescences.
Rhododendron campylocarpum is very common in the Khumbu area, eastern Nepal, where these pictures were taken. In the upper picture, the peaks of Nuptse (7879 m, at left), Sagarmatha (Everest) (8850 m, centre), and Lhotse (8511 m) are seen in the background. (Photos copyright © by Kaj Halberg)
Rhododendron ciliatum is a small shrub, whose white or slightly pinkish flowers have five notched, overlapping lobes. This species has a very limited distribution, from eastern Nepal to Bhutan. It often grows on rocks, at altitudes between 2,700 and 3,900 metres.
Rhododendron ciliatum, Barun Valley, eastern Nepal. (Photo copyright © by Kaj Halberg)
Rhododendron thomsonii grows in open areas, preferably near streams, distributed from between eastern Nepal to south-eastern Tibet. It is easily identified by its red calyx and wax-like flowers.
These pictures are from the Ghunsa Valley, eastern Nepal, where Rhododendron thomsonii is quite common. (Photos copyright © by Kaj Halberg)
Rhododendron cinnabarinum has long, tubular, waxy, pendent flowers, which are usually dark red. This species grows at altitudes between 3,200 and 4,000 metres, from eastern Nepal eastwards to south-western China.
Usually, the flowers of Rhododendron cinnabarinum are dark red, but occasionally paler flowers are seen, as in the lower picture. This species is common in the Ghunsa Valley, eastern Nepal, where these pictures were taken. (Photos copyright © by Kaj Halberg)
Dense thickets of Rhododendron anthopogon, in Nepal called sun pathi, cover large areas in the Himalaya, at altitudes between 3,000 and 5,100 metres. Dried flowers of this dwarf shrub are utilized as tea, and its branches are burned as incense in temples and on house altars.
Rhododendron anthopogon, Gokyo Valley, Khumbu, eastern Nepal. (Photo copyright © by Kaj Halberg)
This man from the Gosainkund area of central Nepal shows a tray, full of dried sun pathi flowers. (Photo copyright © by Kaj Halberg)
The alpine zone in the Himalaya, above the tree limit, is home to several species of dwarf rhododendron, among these Rhododendron setosum and R. nivale, both of which are distributed from western Nepal eastwards to south-western China. They are quite similar, but the leaf margin of R. setosum usually has bristles, and its funnel-shaped corolla is reddish-violet (rarely pink), whereas R. nivale has darker violet, smaller flowers, and no bristles on its leaves. Generally, R. nivale grows in drier areas than R. setosum.
Rhododendron setosum (top) and R. nivale (lower two pictures), both photographed in the Khumbu region, eastern Nepal. (Photos copyright © by Kaj Halberg)
Joseph Dalton Hooker (1817-1911) was a British botanist, who, during the period 1848-1850, described no less than 22 new rhododendron species from Sikkim. The gorgeous Rhododendron dalhousiae was named in honour of the wife of the governor-general at that time, Lady Dalhousie.
This epiphytic species displays a profusion of lemon-coloured flowers, which later turn yellowish-white. It has a rather limited distribution, found from central Nepal eastwards to Arunachal Pradesh, north-eastern India.
Rhododendron dalhousiae, photographed near Tashigaon, Arun Valley, eastern Nepal. (Photo copyright © by Kaj Halberg)
Rhododendron lindleyi is another epiphyte, very similar to R. dalhousiae, but with pure white flowers. It is found in forests between eastern Nepal and Myanmar.
Rhododendron lindleyi, Ghunsa Valley, eastern Nepal. (Photo copyright © by Kaj Halberg)
Rhododendron wightii which grows to four metres tall, forms shrubberies many places in the eastern Himalaya, between 3,300 and 4,300 metres altitude. Its leaves are large, to 20 centimetres long, with felt-like, rusty hairs beneath, and its bell-shaped flowers are white or very pale yellow, with crimson blotches within.
Rhododendron wightii, Barun Valley, eastern Nepal. (Photos copyright © by Kaj Halberg)
Montane areas of Borneo hold c. 55 species of rhododendron, about half of these found on the highest peak on the island, Gunung Kinabalu (4094 m). – Read more about flora and fauna on this mountain elsewhere on this website, see Travel episodes: Borneo 1985 – A hike up Gunung Kinabalu.
Two species are quite common in the forest at about 2,000 metres altitude on Gunung Kinabalu, the pink-flowered Rhododendron brookeanum (now often regarded as a subspecies of the widespread R. javanicum) and the yellow-flowered Rhododendron retivenium. (Photos copyright © by Kaj Halberg)
At higher altitudes, shrubs of Rhododendron ericoides are found. This species has red, funnel-shaped flowers and tiny leaves, reminiscent of those of crowberry (Empetrum nigrum). (Photo copyright © by Kaj Halberg)
In North America, 27 rhododendron species are found, with the highest concentration found in the eastern part of the continent, mainly in the Appalachian Mountains.
The pinxter-flower (Rhododendron nudiflorum), also called R. periclymenoides, is distributed from Massachusetts south to North Carolina, and westwards to western Kentucky and eastern Tennessee.
Pinxter-flower, photographed at Pohatcong Creek, New Jersey. (Photo copyright © by Kaj Halberg)
Flame azalea (Rhododendron calendulaceum) is native to the Appalachian Mountains, from Pennsylvania and Ohio south to Georgia and Alabama. Due to its gorgeous flowers, it is widely cultivated elsewhere.
These flame azalea in Maudsley State Park, Massachusetts, are escapes from earlier cultivation. (Photos copyright © by Kaj Halberg)
Cumberland azalea (Rhododendron cumberlandense) is quite similar to flame azalea, but flowers and leaves are smaller, and when mature, the leaves have a waxy bloom on the underside. Its style and filaments are brick-red, whereas they are yellow, orange, or pink in flame azalea. Cumberland azalea has a limited distribution, found from the Cumberland Plateau in Kentucky south to Georgia, Alabama, and North Carolina.
Cumberland azalea, Cades Cove, Great Smoky Mountains National Park, Tennessee. (Photo copyright © by Kaj Halberg)
Catawba rhododendron (Rhododendron catawbiense) is very common at higher altitudes in the southern part of the Appalachian Mountains.
Catawba rhododendron with raindrops, Pisgah National Forest, North Carolina. (Photo copyright © by Kaj Halberg)
Pinkshell azalea (Rhododendron vaseyi) has an extremely limited distribution, found only in the Appalachian Mountains in North Carolina.
Following a heavy shower, these pinkshell azalea flowers in Pisgah National Forest are covered in rain drops. (Photo copyright © by Kaj Halberg)
As its name implies, the Pacific rhododendron (Rhododendron macrophyllum) is distributed along the North American Pacific Coast, from Monterey Bay in California, north to British Columbia. It is mainly coastal, but is also found rather far inland in the Cascade Mountains of Oregon, Washington, and British Columbia.
Pacific rhododendron, photographed near Trinidad, California. (Photo copyright © by Kaj Halberg)
Europe, including the Caucasus, is home to 12 rhododendron species.
The commonest European rhododendron is the rusty-leaved alpenrose (Rhododendron ferrugineum), which is found in the Pyrenees, the Alps, the Jura Mountains, and the northern part of the Apennines. This species often covers large areas of mountain slopes between 1,600 and 2,200 metres altitude, especially on acid soil. It was named after a rusty-coloured layer of hairs, covering the underside of its leaves.
The rusty-leaved alpenrose often covers large areas of mountain slopes, as here in the Grossglockner area, Austria. (Photos copyright © by Kaj Halberg)
Another common European species is the hairy alpenrose (Rhododendron hirsutum), growing on carbonate-rich soils in the Alps, from Switzerland eastwards, and in the Carpathians, where it may be introduced. It is easily identified by its ciliate leaves. Where the distribution of this species and the rusty-leaved alpenrose occasionally overlap, hybrids between them are frequent.
Hairy alpenrose, Berner Oberland, Switzerland. A common spotted orchid (Dactylorhiza maculata ssp. fuchsii) is also seen in the upper picture. (Photos copyright © by Kaj Halberg)
Rhododendron ponticum is native to the Caucasus, Bulgaria, Turkey, Lebanon, Spain, and Portugal. In 1763, it was introduced to Britain, where it quickly became naturalized, spreading by suckers on the tips of the branches. Today, it is a widespread menace, replacing local plant species, especially in Ireland.
Rhododendron ponticum, photographed near the town of Espiye, on the Turkish Black Sea coast, where it is a native. (Photos copyright © by Kaj Halberg)
Previously, species of Labrador tea, or muskeg tea, were placed in a separate genus, Ledum. However, recent DNA analyses have revealed that they are in fact rhododendrons.
Northern Labrador tea (Rhododendron subarcticum), photographed on the Chukotka Peninsula, eastern Siberia. In former days, this species was known by various names: Ledum decumbens, L. palustre ssp. decumbens, and L. tomentosum. (Photo copyright © by Kaj Halberg)
Western Labrador tea, or trapper’s tea (Rhododendron neoglandulosum), encountered in Kruse State Forest, California. Previously, this species was called Ledum glandulosum. (Photo copyright © by Kaj Halberg)
Dwarf alpenroses, comprising between 2 and 4 species, differ in certain characters from rhododendron species, and they have been placed in a separate genus, Rhodothamnus. These plants are found from Europe across northern Asia to Kamchatka.
The Eurasian dwarf alpenrose (Rhodothamnus chamaecistus) is found in the central and eastern Alps, here photographed at the Passo di Valparola, Dolomites, Italy. (Photo copyright © by Kaj Halberg)
Rhododendron flowers are appreciated all over the World for their beauty.
This woman in the Wumeng Shan Mountains, Guizhou Province, China, has just picked fresh rhododendron flowers and leaves, held by her small son. (Photo copyright © by Kaj Halberg)
Little children in eastern Nepal, one with an armload of Rhododendron arboreum flowers. (Photo copyright © by Kaj Halberg)
(Uploaded August 2017)