Angraecums 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. 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 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 an example of mutual dependence of an orchid and a specific pollinator. ==Taxonomy==