General characteristics of the rhododendron plant, interesting notes, a description of the most popular species and their varieties.
Rhododendron (Rhododendron) is part of the extensive Heather family (Ericaceae). If we talk about the number of the genus, then according to various sources it ranges from 800 to 1300 units, while there are approximately 3000 different garden forms and varietal variations. Almost all of them are evergreens, but there are both semi-deciduous and deciduous varieties in the genus. Basically, representatives of the genus have a shrub form of growth, but occasionally take tree-like outlines. In nature, rhododendrons are widespread in the Northern Hemisphere, on lands dominated by a temperate and subtropical climate. However, some of them grow in the southern regions of China, in the Himalayas and Japan, they are not uncommon in the southeastern regions of Asia and even on the North American continent. In the southern hemisphere, these plants are settled on the island lands of New Guinea and in northeastern Australia.
The rhododendron got its name due to the outlines of flowers, which are somewhat reminiscent of open roses. Therefore, combining the two Greek words "rhodon" and "dendron", this representative of the flora was referred to literally as "rose tree" or "tree with roses."
All types of rhododendrons are quite diverse in their height parameters. There are some that do not exceed 30 cm and take the form of creeping shrubs, but there are specimens reaching a 4-meter mark in the form of trees. There are species that can be grown indoors (well known to many azalea and camellia growers) or suitable for cultivation exclusively in the garden. Such plants grow very slowly, especially in the early years. The root system is located close to the soil surface, has a compact shape and is composed of a large number of fibrous roots.
Leaves vary greatly in size and shape. Leaf plates in rhododendrons are both perennial and biennial or annual. Leaves are attached to the branches, both with the help of petioles in the next order, and they grow sessile. Basically, the foliage is whole-edged, occasionally with a serrated edge. The shape of the leaves is ovoid or obovate, pubescence is present on the surface or they are completely bare, glossy. Even without flowers, foliage is also a decoration of a plant - a rich bright green color, when the leaf plates are young, gradually taking on a dark green color.
However, it is the flowering that is the real pride of planting rhododendron. Flowers are bisexual, characterized by corollas not too regular in shape. Often they can reach 20 cm in diameter at full disclosure. The color of the petals in the corolla takes on snow-white, yellow, pinkish, red, lilac or crimson-violet shades. There are species in which the petals are two-colored or on their surface there is a pattern of specks or strokes. The shape of the corolla also directly depends on the species and variety, so it can take the shape of a bell, tubular or wheel-shaped. Corymbose or racemose inflorescences are collected from flowers. Rarely, buds on branches grow in pairs or singly. Flowers can often have a pleasant scent.
After pollination in the period from September to the end of October, the fruits of the rhododendron begin to ripen, represented by polyspermous capsules, characterized by the presence of five valves. When the fruits are fully ripe, they open from top to bottom. Such boxes are painted in a rusty-iron shade. The fruits are filled with seeds, the length of which varies from 0.5 to 2 mm. The seeds are rod-shaped.
Scientists have conditionally divided all types of rhododendrons into the following groups:
or Lepidote Group), combined species and varietal variations, characterized by the presence of small scales on leaf plates, and small foliage. Sharpness is characterized by both the apex and the base. The foliage is evergreen or semi-evergreen. It happens that not only scales are present on the leaves, the presence of fringed hairs is also noted there. The arrangement on the tops of the shoots of leaves in such rhododendrons is not as dense as in groups including other varieties. An example here are: Greenlandic rhododendron (Rhododendron groenlandicum), Lapland (Rhododendron lapponicum), as well as Rhododendron minus and others.
or Elepidote Group, in which there is no scaly on the leaves, and the sizes of the leaf blades themselves differ in large parameters. However, this also includes azaleas that do not have large leaves. The following types of rhododendrons of this group can be: Rhododendron alabama (Rhododendron alabamense) and white-flowered (Rhododendron albiflorum), treelike (Rhododendron arborescens) and marigold (Rhododendron calendulaceu), as well as rhododendron Vasey.
There is a division into:
- Clumpy hairy which are evergreen varieties. Their leaves with a leathery surface, reaching a length of 4-30 cm. However, in the grayish-yellow rhododendron (Rhododendron sinogrande Balf. F. Smith), they are even longer, and sometimes shorter, like the Forrest rhododendron (Rhododendron forrestii Balf. F. Ex Diels). The front surface of the leaves of such rhododendrons is often bare, glossy and shiny, the reverse is characterized by tomentose pubescence or may be bare. The edge of the foliage is often wrapped. Near the clumpy pubescence, glandular can also be found.
- Fringed-hairy mostly deciduous species. The leaf plates are soft, 2–10 cm long, with the upper and lower sides characterized by a bare surface or pubescence. The foliage of these rhododendrons can also be semi-evergreen, then its surface becomes leathery, like parchment. The length of the leaf plates will vary within 0.5–5 cm. Often, they contain, in addition to fringed, glandular hairs.
This division was carried out by the renowned expert in the study of rhododendrons and breeder Richard Kondratovich (1932-2017). The presence or absence of pubescence on the leaves was taken as a basis. The scientist used the classification of A. Goff, which formed the basis of the above grouping.
Read also recommendations for planting and caring for a lumbago in the open field
Interesting notes about the rhododendron flower
For a long time, the "tree with roses" was known to folk healers, and today it is recognized as official medicine. There are such varieties of varieties of rhododendron (golden (Rhododendron aureum), Daurian (Rhododendron dauricum), Adams (Rhododendron adamsii), Caucasian (Rhododendron caucasicum)), in which scientists have identified the following active substances: andromedotoxin and ericolin and rhodium, as well as arrinodine. The leaves are filled with ascorbic acid, while its concentration reaches its peak in the summer. Therefore, drugs are often prepared from the plant that have not only diaphoretic and antibacterial effects, but also contribute to anesthesia, reduce fever and have sedative properties. Medicines help to remove excess fluid from the body, eliminate swelling and shortness of breath, enhance the activity of the heart muscle, and lower blood pressure (venous or arterial).
With all this, there are contraindications for the use of drugs based on rhododendron, namely:
- serious kidney disease;
- with tissue necrosis;
- any period of pregnancy and lactation.
At the first use, you should consult your doctor.
Many varieties of rhododendron can be toxic to humans due to the content of andromedotoxin, which is often referred to as acetylandromedol or rhodotoxin. That is, these substances are part of neurotoxins and are capable of first strongly excite the nervous system, and then bring it into a depressed state, leading to death.
Description of the species and varieties of rhododendron
Rhododendron dahurian (Rhododendron dahuricum)
The natural distribution area falls on rocky territories and coniferous forests, which are inherent in the regions in northeastern China and eastern Siberia, the plant is not uncommon in the Primorsky Territory and Korea, this also includes the North Mongolian lands. It is characterized by the type of evergreen shrub with medium height parameters. The shoots are highly branching, reaching a height of 20–40 cm. The bark on the branches is gray, they are directed upwards. Thin shoots have a brownish-red tint of the bark, and closer to the tops there is a pubescence of short villi.
The leaf plates of the Daurian rhododendron are characterized by a leathery surface, while their upper side seems to be polished, and the reverse has scaly. The color of young foliage is pale green, gradually giving way to a dark emerald color scheme. With the arrival of autumn days, the leaves take on a greenish-red or brown tone. During the winter months, only a small fraction of the deciduous mass can fly around.
The flowering process lasts 20 days, and is particularly splendid. Flowers open before leaves begin to unfold. The size of the flowers is large, while the diameter is 4 cm. The shape of the corolla of the Daurian rhododendron is funnel-shaped. The color of the petals is pink-purple. Occasionally, in the autumn months, flowering can occur a second time. The species is characterized by increased resistance to temperature drop, excellent reproduction is carried out by means of green cuttings. There are two types of Daurian rhododendron:
- Evergreen form characterized by a dark green color of leaves, petals in flowers of a lilac-crimson hue;
- Garden early hybrid, which is a low-growing bush with lush flowering. The buds begin to open very early. The diameter of the flower is 5 cm, the petals are bluish-red. However, frost resistance is less low when compared with the base species.
for growing in nature, it prefers slopes of stones and mountainous forests, common in the Far East and in the northeast in the foothill regions of Tibet. The height parameters of such a shrub are about half a meter. Branches are highly branched. Throughout their length, there is a pubescence composed of glandular villi. The leaf blades have a dull surface, a rich green color. The foliage is elongated-elliptical in shape, while the length and width parameters are about 2 cm. On the outside, the leaves are bare, on the back, scales are distinguishable, giving it a reddish tint.
Flowering is colorful, in its process corymbose inflorescences are formed, numbering 7-15 buds. When the flower is fully opened, its diameter is 1, 5 cm. The color of the petals takes on a variety of shades of pink. The plant is included in the Red Book of Buryatia.
Japanese rhododendron (Rhododendron japonicum)
The specific name indicates the territory of natural growth - Japan, but more precisely the island of Honshu. In those regions, the bushes prefer well-sunlit mountain areas. Quite a spectacular deciduous plant, reaching a height of 2 m. The branches may have a bare surface or they have pubescence composed of silvery bristles. The color of the oblong-lanceolate leaves is green. The front side of the leaves is glossy, the back has soft pubescence. With the arrival of autumn, the foliage becomes a reddish-orange color scheme.
The racemose inflorescences of the Japanese rhododendron can contain 3-6 pairs of flowers. When blooming, a fragrant aroma spreads around. The corolla of the flower is bell-shaped, while its diameter reaches 8 cm. Petals with a red-scarlet or orange tint. The species is characterized by high resistance to frost, can propagate both with the help of seeds and by cuttings. Most popular when cultivated in mid-latitudes.
Caucasian rhododendron (Rhododendron caucasicum)
The specific name - Caucasus - indicates the territory of natural growth. Shrub with evergreen foliage. Its height is small, as the branches are creeping. Leathery leaves, painted in a dark emerald color, unfold on them. The leaves are attached to the shoots by means of thickened long petioles. The shape of the leaf plates is oblong-oval. The upper side of the leaves is bare, the back has a red tomentose pubescence.
During flowering, racemose inflorescences are formed on peduncles with a hairy covering, in which 4–5 pairs of flowers are connected. They are characterized by a fragrant aroma. The corolla takes on a funnel-bell-shaped shape. It is painted in a pale greenish tint, the inner part has a pattern of green spots. The most popular are the following decorative forms of the Caucasian rhododendron:
- pink-white characterized by flowering earlier than that of the base species;
- shiny with dark pink color of petals in flowers;
- golden yellow characterized by yellow petals with mottling of a pale green color;
- straw yellow in which, when flowering, yellow flowers open, on the surface of the petals with a pattern of specks of a light red tone.
Rhododendron hybrid (Rhododendron hibrid)
in itself combines varieties-forms and hybrid variations grown by gardeners. He is often even called Garden rhododendron. We present the varieties that are most popular when cultivated in open field conditions:
- Alfred - a cultivar of German origin, obtained by robots by crossing the Rhododendron catawbiense and the Everestin variety. The form is shrubby with evergreen foliage, the height of the branches of the plant does not exceed 120 cm. The girth of the crown can be measured one and a half meters. The foliage has a dark emerald color and glossy surface. Its shape is oblong-elliptical. When flowering, dense inflorescences are formed, composed of 15–20 buds. In open flowers, corollas are measured in diameter 6 cm. The color of the petals is saturated crimson, there is a speck of greenish-yellow color.
- Blue Peter is the result of hybridization of the Pontic rhododendron (Rhododendron ponticum). One and a half meter high shrub. The crown is beautiful and spreading, it can be 2 m in diameter. When the flower is fully open, the diameter of its corolla reaches 6 cm. The petals of flowers are lavender-blue, they are decorated with a corrugated edge, while the decoration of the upper petal is a mark of dark crimson color.
- Jackson was bred by English breeders as a result of hybrid work with the Caucasian rhododendron (Rhododendron caucasicum) and the Nobleanum variety. The form of growth is shrubby, characterized by a two-meter height, with a crown of three-meter diameter. There is also a low-growing form, the branches of which will not exceed a height of 0.8 m. The leaves are leathery above, with an oblong outline. Emerald foliage with a matte surface, from the inside it has a brown tint. It blooms with pink inflorescences, which gradually acquire a whitish color, moreover, one of the petals has a yellowish white speck. The inflorescences are composed of 4–6 pairs of buds.
- Rose Marie is a variety developed by Czech breeders who crossed Rhododendron decorum and Pink Pearl. The size of the shrub reaches 120 cm, and the span of the crown is close to 150 cm. Above, the foliage is leathery, the plates have an elongated-oval shape. The upper side of the leaves of an emerald color, has a waxy coating, from the inside the leaf is greenish-blue, also glossy. The edge of the petals is of a pale pinkish hue, which gradually turns into the general background of the petal of a deep pink color with a crimson tint towards the base. The inflorescences are characterized by a compressed shape in the form of a ball, composed of 3-7 pairs of flowers.
- New Zambla bred by Dutch breeders when crossing the Rhododendron catawbiense with the Parsons Gloriosu variety. The height of the loose crown of this shrub reaches 3 m, its girth approaches the mark of 3.5 m. The growth of the stems is almost vertical. On them are leathery sheet plates with a glossy surface of rather large sizes. The inflorescences are dense, containing 10-12 buds. The flowers are also large, reaching 6 cm in diameter when fully opened. The color of the petals is red, with a speck of black color.
- Cunningham's White represented by Scottish breeders and is a cultivar of the Caucasian rhododendron species (Rhododendron caucasicum) enjoying great popularity. The height of the bush does not exceed two meters, the crown girth is approximately one and a half meters. The leaf plates have a skin-like surface, measuring about 6 cm in length and 3 cm in width. The inflorescences are compacted, bearing a dozen buds. The petals of the open flowers are snow-white in color, there is a yellow speck on the surface.
You can find out about the rules of agricultural technology for rhododendrons in a personal plot in our article "Rhododendron: tips for planting and care in open ground".