The genus Angraecum, abbreviated as Angcm in horticultural trade, common name Angrek (Indonesian and Malay) or Comet Orchid, contains about 220 species, some of them among most magnificent of all orchids. They are quite varied vegetatively and florally and are adapted to dry tropical woodland habitat and have quite fleshy leaves as a consequence. Most are epiphytes, but a few are lithophytes.
Tropical Africa and Madagascar contain the majority of the genus with one outlier found on Sri Lanka, and three species once thought to belong to the genus in Japan and the Philippines. But these orchids can also be found on the Comoros, the Seychelles, and the Mascarenes. They occur between sea level and 2,000m in humid regions.
The long-lasting flowers are racemose and grow from the leaf axils. They are mostly white, but a few are yellow, green or ochre. They all have a long spur at the back of the labellum (lip).
In the case of Angraecum sesquipedale, a species from Madagascar, on observing the 30cm spur in the lip, Charles Darwin made the hypothesis that, since the nectar was at the bottom of the spur, a pollinator must exist with a tongue at least that long. Otherwise the orchid could never be pollinated. At the time, he was not believed. However, in 1903, the predicted pollinator was discovered, a hawk moth then named Xanthopan morganii praedicta ("praedicta" meaning "the predicted one"). It has an appropriately long proboscis. The specific name sesquipedale means "one foot and a half", referring to the length of the spur. This is a perfect example of mutual dependence of an orchid and a specific pollinator.
Growing Angraecums
In the right conditions these orchids are healthy and require little attention. As they are epiphites the potting mixture should be loose and free draining. Prolific roots are formed from the base and also amongst the lower half of the foliage. These are attractive although somewhat troublesome when moving plants to and from shows. Once your angraecum is big it is best to pot it in a heavy terracotta pot or place a brick in the bottom of the pot in order to ensure your beauty does not get top heavy and risk snapping when blown over in the wind (especially since they flower during the windier times of the year, this can be very sad). When watering a good soaking with a hose or watering-can is best (not just a misting from a spray gun) as this helps to flush away any salts from fertilizers that may be present in the potting mixture and also thoroughly wets the plant. Make sure the roots halfway up the stem get a soaking too, not just the potted roots. This is a great orchid and will give you years of pleasure. They're slow growing and require little attention. They’re very hard to kill.
Source, Images: http://en.wikipedia.org/wiki/Angrec
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