Delayed autonomous self-pollination in two Japanese varieties of Epipactis helleborine (Orchidaceae)

The terrestrial orchid Epipactis helleborine is a morphologically variable species with a wide geographical distribution. It is found throughout Europe and continues eastwards to Siberia, China and Japan. It is usually pollinated by social wasps and displays the morphological characteristics of an outcrossing species. In warm, temperate areas of Japan, E.helleborine often appears in alpine or subalpine regions, and has never been found in low-altitude forests, except for coastal pine forests. The coastal population of E.helleborine is often classified at the variety level, as E.helleborine var. sayekiana, and the inland populations are known as E.helleborine var. papillosa. It is possible that E.helleborine var. sayekiana possesses a distinctive selfing strategy, as its autonomous self-pollination has evolved in dry habitats, such as coastal dunes. The present study investigated the pollination biology of E.helleborine var. sayekiana and var. papillosa to detect differences in their reproductive systems. Unexpectedly, both E.helleborine var. papillosa and E.helleborine var. sayekiana were found to possess a self-pollination strategy and were therefore rarely visited by insects. Self-pollination occurs at the end of the flowering season and probably acts to ensure pollination even if insect-mediated pollination fails. Moreover, there are no floral differences between E.helleborine var. papillosa and E.helleborine var. sayekiana. These observations suggest that it is not necessary to distinguish between these two varieties. Furthermore, E.helleborine var. papillosa was pollinated by hoverflies, suggesting that E.helleborine var. papillosa is probably biologically distinct from its mother species, E.helleborine.(c) 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173, 733-743.