Rhododendron

History

At the time medieval, the rhododendron was called “Rosage”, term which was preserved until the 18th century, since Joseph Pitton de Tournefort introduced in 1702 the “Rosage of the Black Sea”, following a voyage in Asia Mineure. It is to the naturalist Carl von Linné that one owes the denomination of Rhododendron.

The rhododendron started by being really cultivated like horticultural species by John Tradescant in 1656, which brought back a Rhododendron hirsutum of the Alps. However, the real success of the rhododendron started with the species of origins Himalayan and Chinese ( Rhododendron auriculatum and seroticum ) in the middle of the XIX century.

Description

The rhododendrons are generally plants forming of the spread out shrubs or round-offs, sometimes of the trees being able to make up to 15 meters in height (in particular in the Himalayas). They are generally Sempervirent S, although the azaleas have sometimes sheets Caduque S. the foliage is green dark.

They are plants extremely Acidophile S, which one sometimes gathers under the generic term of plants of Ground of heather. However, certain rhododendrons agree to be cultivated in ground S neutrals, even slightly limestones ( Rhododendron hirsutum ).

The Fleur S, in the shape of widened trumpet, can be pink, white, pink lilacé, mouchetées of crimson, pink salmon, carmine. The flowers can open out since September (for the hasty shapes of apartment), but more generally January/February until the end of July (for the latest forms). The largest flowers are of approximately 10 cm length and broad and grouped in large conical final inflorescences and great number.

The majority of the rhododendrons do not release any perfume. However, some botanical forms ( Rhododendron auriculatum, bullatum, crassum, decorum, fortunei, grifithianum, polyandrum , etc) are scented.

Varieties

The Rhododendron kind is very diverse. It gathers nearly 1000 species, of which some are true rhododendrons (large flowers) and others of the azaleas (with small flowers, cash with more 5 cheesecloths) (les two forming botaniquement part of very the groupe).

One differentiates:

hasty varieties with a flowering at the end of April - at the beginning of May
varieties of average season with a flowering in May
late varieties with a flowering at the end of May - at the beginning of June

The hybrid rhododendrons with large flowers are shrubs in general being able to reach 2 to 3 m but with a rather slow growth.

The dwarf rhododendrons are hasty hybrids which do not exceed 1 m in height, and are ideal plants for rubble.

The rhododendrons known as giant are trees being able to reach 15m top. One finds them mainly in the Himalayens countries: Nepal, Sikkim, Bhutan. The Himalayan chain and the close areas (Burma, Tibet, Yunnan) are known for the extraordinary richness of their flora in rhododendrons. The peninsula Indo-Faintness and the New Guinea accommodate as for them more than 300 tropical species, of which many épiphytes.

The Rhododendron simsii is more known under the name of azalea with persistent foliage. It is originating in China and Japan. It is an ideal species for the apartments, with a flowering from September to May.

Another known rhododendron is the Rhododendron vaccinietum . It is typical alpine stage higher, for which it represents the transition between the Alpine Conifère S and pastures.

Culture

The rhododendrons can support the full sun but an excess of sunning is likely to cause the yellowing of the sheets and the appearance of brownish spots on the exposed part. They are also very sensitive to the reverberation of the walls. They appreciate especially the light shade or the protection of larger plants. They can be used against a wall exposed to north.

The fibrous roots remain grouped with the foot of the plant and thus allow the transplantation of the oldest subjects. The rhododendron is a ground plant of heather and particularly fears limestone even in minor amount, it fears even the limestone contained in the water of watering.

The rhododendrons adapt with all the plants known as " of ground of bruyère" and can be cultivated in staged solid mass.

To obtain the best results, it is necessary to take care to withdraw all the flowers faded at the conclusion of flowering. This makes it possible to avoid the development of seeds, and supports the new growths and the flowering of the following year. It is also necessary to sprinkle copiously, preferably with rainwater, during flowering and until the beginning of August.

Toxicity

According to certain sources, honey coming from the flowers of certain rhododendrons of Asian origin would cause intestinal disorders. Indeed, the plant contains in its sheets a strongly emetic glucoside. Thus Xénophon (430 to 355 before J. - C.) described in the Anabase the odd behavior Greek soldiers, the Ten Thousand, having raid the honey of a village surrounded by rhododendrons. All those which ate some lost the reason, vomitted, had the diarrhea and lost their forces. Those which had eaten some little were simply drunk. Nobody died however: at the end of the 24 hours, the Greeks found the reason and 4 days later they held again upright.

Four centuries later, the same mishap arrived at the armies of Pompée: Pline Old the announces that troops were victims of a honey which makes insane.

The rhododendron concerned was kind Rhododendron ponticum . Later, it was recognized that honey resulting from this azalea had effects slightly Hallucinogène S and Laxatif s.Le Rhododendron ponticum at the origin of the digestive disorders contains andromédotoxine (alcohol diterpenic), the rhododendron of the Alps ( Rhododendron ferrugineum ) of the arbutine, aricoline and rhodoxanthine. These two rhododendrons are regarded as plants of average toxicity, but which cause vomiting, various digestive disorders, nervous, respiratory and cardiovascular disorders.

Others

Language of the flowers

The significance of the rhododendron is that of the danger; this significance is most probably related to the presence of toxic compounds.

The significance of the azalea is that of the Tempérance.

External bonds

The German Company of the Rhododendrons (of) (Fr) (in)

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