Floral miniaturisation and autogamy in boreal-arctic plants are epitomised by Iceland’s most frequent orchid, Platanthera hyperborea

• Published in: PeerJ
• Main Authors: Richard M. Bateman, Gábor Sramkó, Paula J. Rudall
• Format: Article in Journal/Newspaper
• Language: English
• Published: PeerJ Inc. 2015
• Subjects: Allometry; Autogamy; Baker’s rule; Functional constraint; Iceland; Endemism; Medicine; R; Arctic
• Online Access: https://doi.org/10.7717/peerj.894; https://doaj.org/article/9931d363a8344d4887c199c74f8c417c

Background and Aims. This paper concludes our series of publications comparing island and mainland speciation in European butterfly-orchids, by studying the morphology, phylogenetics and reproductive biology of the controversial circum-arctic species Platanthera (Limnorchis) hyperborea—the most frequent of seven Icelandic orchids. We draw particular attention to its phylogenetic placement, remarkable reproductive biology and morphological convergence on other Platanthera lineages through floral miniaturisation.Methods. Five populations of P. hyperborea in southwest Iceland were measured for 33 morphological characters and subjected to detailed multivariate and univariate analyses, supported by light and scanning electron microscopy of selected flowers. Representative samples from six populations were sequenced for nrITS and placed in a taxonomically broader phylogenetic matrix derived from previous studies.Key Results . Section Limnorchis consists of three distinct ITS-delimited clades based on P. stricta, P. sparsifolia–limosa–aquilonis and P. dilatata–hyperborea. Within the latter group, supposed species boundaries overlap; instead, the data indicate a crude stepwise series of ribotypic transitions extending eastward from North America to Iceland. Morphometric data failed to identify any taxonomically meaningful partitions among Icelandic P. hyperborea populations, despite the presence of a distinct and apparently plesiomorphic ribotype at the most glacially influenced habitat sampled. Microscopic study of the flowers revealed several distinguishing features (some not previously reported), including resupinate lateral sepals, toothed bract margins, club-shaped papillae shared by both the interior of the labellar spur and the stigmatic surface, and an exceptionally adhesive stigma that is reliably covered in disaggregated pollen masses prior to anthesis; auricles are absent.Conclusions. Ribotypes suggest that Icelandic P. hyperborea represents the terminus of a migration route that may have begun in East Asia ...