AngraecumThe Angraecum orchids, or Comet Orchids, are a very interesting genus of plants. Most come from Africa or Madagascar, though a few species come from other places. The most famous species is the Christmas Orchid, Angraecum sesquipedale. These plants are monopodial, so there's a single stem which grows upward with alternating leaves, and flower stems and roots emerge from just above the leaves. Occasionally the stem will branch. (Some species do this more than others.) They generally grow as epiphytes, but a small number of species grow lithophytically as well. Vegetatively, the plants vary widely; some are very small, others are very large; some grow upright, others hang downward. It's very hard to generalize, other than to say that they are all monopodial. They are pollinated by moths: the white color of most species makes them more visible at night (most moths are nocturnal), and the flowers are also fragrant at night. (Both of these adaptations to moth pollinators are also common in Brassavola orchids, a conspicuous example of convergent evolution that Charles Darwin didn't know about during his famous investigation of Angcm. sesquipedale.) Some species have one flower per inflorescence, while others produce several.
Image courtesy of scott.zona
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