Local evolution of obligate autogamy in Epipactis helleborine subsp neerlandica (Orchidaceae)

Isozyme analysis was used to assess the origin of the Danish Epipaetis renzii, a local endemic of open coastal dunes. It seems to have evolved recently in several local populations of the more or less allogamous E. helleborine subsp. neerlandica. The obligately autogamous E. renzii is restricted to the easternmost part of the Danish range of E. helleborine subsp. neerlandica, indicating that transition to obligate autogamy has been a selective advantage in that area. This may be explained by water stress, caused by a higher evapotranspiration (cf. the mean temperature of July which increases towards the cast) - obligate autogamy shortens the time span from anthesis to fruit set due to a rapid pollination process. We propose that E. renzii should only be recognized as a variety of E. helleborine subsp. neerlandica.