How Edith Coleman solved the orchid puzzle of Charles Darwin
A bit more about Cryptostylis erecta.
Edith Coleman was a high school teacher, a keen naturalist who lived in rural Victoria in the early 20th century. As we all know, Charles Darwin was very interested in orchids, has written a book on these plants and has used his observations on orchids to formulate his theory of evolution. During his time, he raised a question about orchid pollination which remained unanswered until the 1920s when Edith Coleman and others came along.
Charles Darwin was puzzled by his observation that some orchid species did not have nectaries but were still visited and pollinated by insects.
Edith Coleman based her observations on three Cryptostylis species, including Cryptostylis erecta and discovered the unique way of pollination perfected by some orchid species, viz. the process of pseudocopulation (false mating). This refers to the pollination of plants by male insects while attempting to mate with flowers that resemble the female insects. All the five species of Cryptostylis in Australia were pollinated by the same insect, the ichneumon wasps.
Judging from the behaviour of the male wasp and the resemblance of the labellum of Cryptostylis flower to the female wasp, she proposed and subsequently proved that the male wasp was attracted to the orchid sexually, mistaking the labellum of the flower to be his female partner and in the process, cross pollination of the orchid was achieved. This happened during a time gap of about 2 weeks before the hatching of the female wasps. Furthermore, Edith Coleman discovered that the male wasps could still locate the orchid flowers even if they were hidden out of sight. Hence, she postulated that the male wasps which had very poor eyesight were also attracted to the orchid by a chemical emitted by the orchid flowers.
The chemical was identified only recently and was found to be identical to the pheromone produced by the female wasps.
This is fascinating work of nature discovery by an Australian. We are also amazed by the report that Edith Coleman carried out some of her experiments using pots of Cryptostylis. She must have been a very good grower of this kind of orchid nearly a century ago!
Cryptostylis erecta –Strickland State Forest NSW
(photo – Sau-wan Chan)
