Himantoglossum hircinum(Lizard Orchid) reviewed in the light of new morphological and molecular observations

Abstract

Himantoglossum hircinum is one of the rarer and more charismatic orchids in the British flora. Morphometric comparison of the two largest and best-known populations in southern England – the coastal dune population at Sandwich and the chalk grassland population at Newmarket – using 46 characters showed that they differ only subtly, the Sandwich plants being on average more vegetatively robust and slightly more darkly pigmented, but possessing less extensive lip-spots and substantially longer ‘arms’. A comparatively morphologically divergent semi-desert population from Ifrane, Morocco differs from the English populations in having broader stems, less recurved ‘arms’, a more strongly down-curved spur and in lacking near-circular spots within the sepals. Molecular comparison of 46 plants, representing 13 English populations and 18 populations from Continental Europe and Morocco, revealed only subtle distinctions in the high-copy nuclear region ITS, and smaller-scale comparisons of the low-copy nuclear (LEAFY) and plastid (four intron) regions proved to be even less discriminatory. These results reinforce prior morphological inferences that H. hircinum is a cohesive species. Scanning electron microscopy elucidated the ontogeny of these remarkable flowers, suggesting that the exceptionally elongate central labellar lobe originated by accelerated heterochronic growth and showing that the characteristic spiral torsion always runs counter-clockwise. Lateral fusion of the paired viscidia is convergent with several other lineages of subtribe Orchidinae. Review of pollination and life-history features of H. hircinum suggest that they are typical of food-deceptive species within Orchidinae. The Lizard Orchid is infamous for geographic mobility; its cycles of expansion and contraction through the last century have been interpreted as reflecting a net northward migration in response to recent climate change. Our data tentatively suggest relatively recent colonisation of Morocco at high altitudes and an overall northwestward direction of migration into the UK. ITS ribotypes indicate multiple immigration events leading to levels of genetic diversity in England comparable with those on the Continent. A non-recent origin is inferred for H. hircinum which, despite recent systematic revisions, may harbour further cryptic species; the taxonomic status of supposed outlying populations in southern Italy in particular is questioned by the present genetic data.