Peter, Epipactis helleborine is not a tropical S.E.Asian plant; I know nothing about it. Maybe someone else on the list has some answers. I'm not enthusiastic about the idea that a growing plant can throw an internal switch and suddenly become autogamous because of some external stimulus .... and I'm even more sceptical that this can be triggered by the lack of an external stimulus. How would the plant know it is growing in a place where there will never be any pollinators ? It would be easy enough to test your hypothesis.... all you'd need is some non-autogamous E. helleborine plants and a greenhouse or large plastic bag.
I suspect that many (most ? all ?) orchid species produce a small percentage of autogamous-form seeds every time they set a capsule. I think it would be fairly easy for a plant to evolve a single gene that leads to autogamy; almost any deficiency in the material of the rostellum would result in the necessary outcome. Such a gene would give the species a valuable evolutionary advantage ... the ability to colonise fresh territory from just one seed, even in the absence of pollinators. Peter O'Byrne Singapore ----- Original Message ----- From: peter croezen To: OGD ; Peter O'Byrne Sent: 09 October 2004 10:43 PM Subject: What triggers for autogamy in orchids Peter who said: > Many authors have noted that when an orchid species progressively > colonises its way from island to island across the ocean, an > autogamous form often leads the way. Very interesting, Peter!! Epipactis helleborine, a European species, can be found in many locations in North America and it is autogamous. Assuming that these plants started from seeds carried on the belongings or shoes of immigrants, did these seeds come from autogamous plants in Europe, or from non-autogamous plants and the total absence of pollinators in NA triggered them into autogamy? Is it known what exactly triggers autogamy? Would total absence of pollinators be a trigger? Are both, autogamous and pollinator dependent, forms of Epipactis helleborine found in European habitats or colonies where pollinators are still plenty? How about other species? What is the natural pollinator of Epipactis helleborine in Europe?
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