× Dactylodenia lacerta (Orchidaceae): a morphologically cryptic hybrid orchid new to science from the Lizard Peninsula, Cornwall

Abstract

We describe the first reported hybrid to occur in nature between Dactylorhiza praetermissa and Gymnadenia borealis as × Dactylodenia lacerta R.M. Bateman & Tattersall. This vigorous plant was found and digitally imaged on a roadside verge of Crousa Downs on the Lizard Peninsula of Cornwall by Barry Tattersall in June, 2016, and tentatively identified as a hybrid new to science. However, detailed morphometric analysis using 40 characters and based partly on the initial images failed to confirm its hybrid origin, suggesting instead that it was a slightly deviant plant of D. praetermissa. Comparison of the hybrid with its putative parents by DNA sequencing of nuclear (ITS) and plastid (trnL-F) regions later confirmed the F1 hybrid nature of the plant, as well as identifying D. praetermissa as the hybrid’s ovule-parent and G. borealis as its pollen-parent. This result contrasted with prevailing theory that pollinators (in this case, most likely bumblebees) should preferentially transfer pollinaria from the shorter-spurred plant to the longer-spurred plant. The Crousa Downs plant is thus best described as a cryptic hybrid that shows strong maternal dominance in inheritance patterns, perhaps reflecting the fact that its ovule-parent is allotetraploid but its pollen-parent is diploid. A brief review of × Dactylodenia hybrids in the British Isles concludes that opportunities for the origin of this particular hybrid are severely limited by the contrasting habitat preferences and geographic distributions of its parents. An ongoing future for this apparently unique plant is unlikely due to local authorities’ inappropriately-timed mowing regimes.

Keywords:

• Dactylorhiza praetermissa
• Gymnadenia borealis
• hybridisation
• ITS
• maternity
• morphometrics
• paternity
• plastid

Acknowledgements

We thank Peter Wood for providing the DNA specimen used. We also thank Peter for permission to reproduce Fig. 1c and the late Derek Turner Ettlinger for (prior) permission to reproduce Fig. 2c. We are grateful to Paula Rudall for rapid and insightful comments. RB would like to conclude by thanking Louise Marsh for her excellent editorial support underpinning the seven papers that he has published in NJB through the last seven years.