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Rhododendron: Benefits, Uses, Effects?

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Rhododendron: Benefits, Uses, Effects?
Morphological characteristics of the genre

arboreoI rhododendron rhododendron shrubs are elegant, sometimes trees.
The leaves are alternate, often close to the top of the branches, whole, annual or biennial cycle and, therefore, the plants have persistent foliage.

The flowers are usually large, from white to red to yellow, in corymbs or false in terminal clusters, rarely solitary. The calyx is variable, generally with five sepals forming a cup as many teeth. The corolla is irregular, sometimes funnel otherwise tubular, with a more or less oblique flap which manifests itself in five lobes. The stamens are eight to ten, the ovary has an elongated thin.

Systematics
The classification of the genus Rhododendron is a nightmare for taxonomists: in addition to being one of the largest in the plant kingdom, has closely allied species to the point that they are more numerous species which are often confused with each other than those who clearly stand out. To get an idea should be to review the professional literature on the subject and, particularly, the work published by the British Society of Rhododendrons.
Natural, therefore, that the number of species ascribed to the genus is reason to dispute: currently about 1,200 known species, but a partial reclassification would reduce the 750. Moreover, some botanists shall refer to three hundred and fifty and two hundred others even only.
Rhododendrons occupy every possible environment: the forest undergrowth, the banks of streams, meadows, mountain ranges, swamps, stains, meadows, cliffs, the rocks, the base and the top of the mountains and the trees themselves often as epiphytes.
The highest segregation of species occurs in the Himalayan region, but typically also numerous in central and western China. Some grow in the wild in the Philippines and twenty are part of the flora of North America. From the East Indies genre goes largely south-eastern Asia, North America to Australia.
The adaptations to different climates so they selected disparate shapes and sizes. The leaves vary from a few millimeters to a meter in length, the flowers go from huge fragrant trumpets and long up to 12 cm of R. nuttallii and large flowers composed of R. sinogrande, both native to South East Asia, to small the flowers of some species of the high mountains of subsection lapponica. By sliding it arrives at rhododendrons rhododendrons del'Himalaya.
Recall that the rhododendrons belong to the family Ericaceae and that many species are divided into two sub-genres:
Eurhododendron, they belong to the species rarely deciduous leaves;
Azalea, characterized by species whose leaves are deciduous, rarely persistent.

Rhododendron, the main species

Himalaya region
R. arboreum, tall tree up to 25 meters, red and pink flowers, early flowering.
R.campanulatum, shrub or tree up to 10 m high, flowers white to purple, all'azzurrino, spotted.
R. falconeri, tall tree up to 12 meters, leaves up to 30 cm long, fleshy cream-colored flowers.
R. thomsonii, tall shrub up to 5 feet, dark red flowers and waxy.
R. cinnabarinum, tall shrub up to 5 feet, pendulous flowers and waxy white, apricot, pink, yellow, dark crimson and purple.
R. nuttallii, reaching 10 meters in height, 12 cm long flowers over yellow cream-colored, usually fragrant.
region of China
R. bureavii, up to 7 meters tall shrub, leaves up to 20 cm long, flowers white to pink, spotted.
R. decorum, goes so far as to Burma, tree 9 meters high, red or pale pink fragrant flowers.
R. fortunei, comes the height of 10 meters, white flowers from pink to lilac-scented. It 's the most fragrant species rustic and resistant up to -28 ° C.
R. neriflorum, tall shrub up to 3 meters, scarlet flowers.
R. sinogrande tree 11 meters high, leaves up to 90 cm long, cream-colored flowers.
R. souliei, shrub 5 meters, from white to pink flowers. It is one of the most beautiful species living in arid environment.
R. campylogynum, spread to Tibet reaches 50 cm, purple flowers from black to creamy white, tubular in shape brought by long stalks.
R. dauricum shrub up to 2.5 meters purposes, deciduous or evergreen, blooms in winter or early spring.
R. dalhousiae, is considered the founder of those rhododendrons in flower lily in shape, color and scent, reminiscent exactly a white lily. It is a woody shrub with leaves petiolate.

Japan
R. metternichii, up to 3.5 meters, 15 cm long leaves, flowers deep pink color, sometimes tinged with blue, resistant to -28 ° C and many forms are also resistant to heat.
India
R. indicum, azalea is the most popular and if they know at least seven hundred different vegetable varieties that are derived from botanical forms of this very polymorphic species, and also by interspecific fertilization with morphologically close species, such as R. ledifolium. Commonly known as Azalea indica is a shrub 1-2 meters high, very branching off, with persistent leaves. The flowers are slightly stalked, solitary, live salmon color, placed at the top of the branches. Among the varieties obtained forty are regularly cultivated and have flowers ranging from pure white to salmon, red, lilac-purple, but also in colors streaked, spotted.

U.S.
R. catawbiense, 3 meters tall shrub native to the eastern regions, lilac flowers, bloom late, resistant to - 40 ° C and is very rustic.
R. carolinianum, comes to 1.8 meters in height, flowers from pink to white, very rustic.
Asia Minor
R. ponticum, especially shrub, 3-4 feet high, with bell-shaped flowers with a diameter of at least 5 cm, purple-violet. And 'the species by hybridization with caucasicum R. and R. catawbiense gave rise to the modern multi-colored rhododendron hybrids. This species has been successfully naturalized in many parts of Britain, becoming a weed that can create problems all'arboricoltura local.
R. caucasicum, known as "rhododendron of the Caucasus", is a compact bush that does not exceed one meter tall, the flowers are white, but pink externally.

The three wild species in Italy
Rhododendron L. ferrugineum
Evergreen shrub with branches brittle, generally rhododendron ferrugineumascendenti. Leaves elliptic, entire, rounded at the apex, glabrous and below ferruginee for the dense glandular scales. The flowers are grouped in short racemes with peduncles 1-2 cm long, calyx very short, red-purple corolla tube 7-8 mm. The aroma is resinous and intense.
This species is characteristic of the subalpine and alpine moorland growing on acid soils. Rises to over 2,300 meters, usually sterile, and Val d'Aosta reaches 3,000 meters. In the area insubrica down in the valley (in the canton of Ticino up to 230 meters). In these positions is present in the chestnut thick and reaches its maximum size. Apennines is rare and limited to the highest peaks of the Tuscan-Emilian Apennines.
Rhododendron hirsutum L.
Similar to the preceding species is distinguished by the leaves that have long lashes on the edge and at the bottom are green and with scattered punctate glands, initially white and then brown. In addition, the corolla is pale pink and almost odorless. Unlike the previous limestone is abundant in the Alps, where she acts as pioneer plant and is easily found on scree and just soaked consolidated. Sale of up to 2,200 meters, rarely to 2,600, spread dwarf shrubs and thickets of dwarf pine and Scots pine. In the Adige valley drops almost to the floor, but, unlike the previous one, always in sunny areas.
Rhodothamnus chamaecistus (L.) Rchb.
According to some botanists this species is considered a separate genus, while others form a section of the genus.
However you consider it is a suffrutex with woody stems, prostrate or ascending. The leaves are elliptical, evergreen. The flowers are at the apex of the branches, corolla rosy.

interest in beekeeping
The wild rhododendrons bloom in Italy in June-July.
The nectar is produced by a thickening of the glandular tissue located inside the tube of the corolla; has a sugar content of 24-30%, with a prevalence of sucrose.
The pollen, as in all the Ericaceae, occurs in the so-called tetrads form subspherical composed by the four pollen grains which, derived from a single mother cell, do not separate. The balls of pollen collected by bees are whitish and small (approximately 6.8 mg).
This plant provides abundant nectar and pollen for bees, brought on by beekeepers nomadic pastures; however, the rhododendron flower honeys are quite rare.
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economic interest
It flowers mainly in the rhododendrons that manifest their economic potential. In the second half of the eighteenth century were introduced in Europe, the first exotic rhododendron (R. ponticum and R. luteum) and the gardeners began to select morphologically and spread numerous species. Much later they began the hybridization between different species and today the market is almost completely dominated by rhododendron is properly said that the hybrid azaleas. Famous are the "Ghent azaleas" born from crosses between the more traditional azaleas, the Chinese, the Japanese and and the pontine and by hybridization with R. calendulaceum, R. nudiflorum, R. canadense etc..
They are the famous azalea blooms on Lake Como and Lake Maggiore, between late May and early June.
A marginal use is related to the curative properties of the leaves, which contain arbutin, ericolina, rodotannico acid, other acids, waxes, and an essential oil with a composition considered poisonous, and that infusion or extraction by oil, are used against skin diseases, diseases of the kidneys and rheumatic pains.
In addition, the galls that form on plants, if harvested between June and August, possess vulnerary properties that allow the extraction of oil for external use.
In the so-called "Swiss tea" come from the other leaves even those of R. ferrugineum, less poisonous than those of the other species.

cultivation
The main requirement is a rhododendron subacido humus soil (pH 6), the land of heather or chestnut or berries, mixed with peat. The soil should also be lightweight, adding sand and manure consumed. There are very few species that are adapted to alkaline soils. The root system, thick and rather superficial, does not require a deep soil; 30-50 cm is sufficient. Important drainage and, therefore, the clearing of the subsoil. To the south the rhododendrons require shady places, while more than 800 meters of sun exposure becomes a necessity.
Generally, both species hybrids stand up well to - 6 ° C.
Rhododendrons normally not pruned, except for the ribs to the young branches and to shape the plants with regular tillering. The subjects are pruned old on old wood to encourage the formation of new buds, operating immediately after flowering. The plants withered dried flowers are removed to prevent the excessive production of seeds affects the formation of flower buds. In poor soils no longer be a useful mulch humus.

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