Darwin’s orchid  (Angraecum sesquipedale)

Listed on Appendix II of CITES (1).

Darwin’s orchid is not only spectacular in appearance but also the subject of probably the most famous story on pollination in orchids (3) (4) (5) (6). Large and robust, it produces one to three star-shaped flowers on each inflorescence, which turn from green to creamy white within a few days of opening in the winter (2) (7). Particularly fascinating is the impressive, almost implausible length of the flowers’ nectar spurs, measuring up to 35 centimetres long (2) (3) (7). The upright, or curving, stem typically grows singularly, and is often bare near the base, but gives rise to a fan of leathery, greyish-green, strapped-shaped leaves higher up. The roots are extensive and usually appear flattened on the surface of the substrate (2) (7).

Darwin’s orchid is endemic to Madagascar, where it is found near the east coast (2) (7).

This epiphytic or lithophytic plant grows on the bark of large trees or on rocks in coastal forests from sea level up to 100 metres (2) (7).

When Charles Darwin received a flowering specimen of Angraecum sesquipedale, he speculated that the plant most be pollinated by a gigantic moth, with an enormous proboscis capable of accessing the nectar collected in the bottom of the long spurs. However, at the time, no such moth was known to science, and so many treated Darwin’s prediction with disbelief and ridicule (3) (4) (6). Darwin’s vindication arrived posthumously, when a hawk moth (Xanthopan morganii praedicta) from Madagascar was discovered in 1903 with a proboscis just long enough to access the nectar (3). Although the relationship between Xanthopan morganii praedicta and Darwin’s orchid has since become a classic example of coevolution, to this day, it has yet to be verified in the field (8).

All of Madagascar’s orchids face loss of habitat through logging and clearance for agriculture, while the most beautiful and rarest species are threatened by over collection for the horticultural trade (9).

Darwin’s orchid is listed under Appendix II of CITES which makes it an offence to trade this species without a permit (1). Fortunately, many specimens available in cultivation have been propagated from seeds rather than collected from the wild (7). Orchid conservation in Madagascar is spearheaded by the Royal Botanic Gardens, Kew, who are raising funds through the Threatened Plants of Madagascar Appeal to establish a local nursery and develop appropriate propagation methods for endangered Malagasy orchids (9).

To find out more about the Threatened Plants of Madagascar Appeal visit:

Royal Botanic Gardens, Kew - Threatened Plants of Madagascar Appeal:
http://www.kew.org/friends/madagascar/index.html

For more general information on the conservation of orchids, visit:

Orchid Conservation International:
http://www.orchidconservation.org

• Coevolution: the evolution of two species in reaction to changes in each other.
• Endemic: a species or taxonomic group that is only found in one particular country or geographic area.
• Epiphytic: a plant that uses another plant, typically a tree, for its physical support, but which does not draw nourishment from it.
• Lithophytic: a plant that grows on rocks or stony soil.
• Pollination: the transfer of pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.
• Proboscis: general term for a trunk-like protrusion from the head or anterior of an animal. It is associated with feeding.
• Spurs: slender tubular projections from orchid flowers; in some orchids the spurs are associated with nectaries.
• Substrate: the object or material on which an organism grows or is attached.

1. CITES (April, 2009)
   http://www.cites.org
2. La Croix, I.F. (2008) The New Encyclopedia of Orchids: 1500 Species in Cultivation.Timber Press, Portland, Oregon.
3. Van der Cingel, N.A. (2001) An atlas of orchid pollination: America, Africa, Asia and Australia.A.A. Balkema, Rotterdam.
4. Thompson, J.N. (1994) The Coevolutionary Process.University of Chicago Press, Chicago.
5. Niklas, K.J. (1997) The Evolutionary Biology of Plants.University of Chicago Press, Chicago.
6. Darwin, C.R. (1862) On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing.John Murray, London.
7. Stewart, J., Hermans, J. and Campbell, B. (2006) Angraecoid Orchids: Species from the African Region.Timber Press, Portland, Oregon.
8. Kitching, I.J. (2002) The phylogenetic relationships of Morgan’s Sphinx, Xanthopan morganii (Walker), the tribe Acherontiini, and allied long-tongued hawkmoths (Lepidoptera: Sphingidae, Sphinginae). Zoological Journal of the Linnean Society, 135: 471 - 527.
9. Rotal Botanic Gardens, Kew (June, 2009)
   http://www.kew.org/plants/orchids/madagascar.html