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

Bateman RM, Sramkó G, Rudall PJ - PeerJ (2015)

Bottom Line: 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.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.When considered in combination with independently derived lineages of Platanthera on the Azorean and Hawaiian archipelagos also bearing small green flowers, our observations show allometric and paedomorphic reductions in flower size as the primary evolutionary driver, but also indicate strong developmental and functional constraints.

View Article: PubMed Central - HTML - PubMed

Affiliation: Royal Botanic Gardens Kew , Richmond , United Kingdom.

ABSTRACT
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 before passing through North America and presumably Greenland. The incohesive pollinia, rapidly desiccating anther locules, weakly developed rostellum, exceptionally adhesive stigma and the close juxtaposition of compact male and female reproductive organs together conspire to cause routine autogamy and frequent cleistogamy, despite the continued production of substantial nectar reservoirs in the spur and consequent ongoing attraction to the flowers of insects, including mosquitoes. When considered in combination with independently derived lineages of Platanthera on the Azorean and Hawaiian archipelagos also bearing small green flowers, our observations show allometric and paedomorphic reductions in flower size as the primary evolutionary driver, but also indicate strong developmental and functional constraints.

No MeSH data available.


Related in: MedlinePlus

Populations of Platanthera hyperborea sampled in southwest Iceland during the present study.Base image also shows the capital Reykjavik, southwestern islands, icecaps and major rivers (courtesy of GoogleEarth). The dashed line in the inset denotes the Arctic Circle.
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fig-1: Populations of Platanthera hyperborea sampled in southwest Iceland during the present study.Base image also shows the capital Reykjavik, southwestern islands, icecaps and major rivers (courtesy of GoogleEarth). The dashed line in the inset denotes the Arctic Circle.

Mentions: Initially, taxonomic discussions were driven entirely by perceived phenotypic complexity (cf. Luer, 1975; Sheviak, 2002; Delforge, 2006), but later became informed by the gradual accumulation of molecular systematic data across the genus (Hapeman & Inoue, 1997; Bateman et al., 2003; Bateman et al., 2009). More focused investigations of North American representatives of Section Limnorchis, most notably those pursued by Lisa Wallace, have revealed considerable genetic complexity, driven in part by allopolyploidy (Wallace, 2002; Wallace, 2003; Wallace, 2004; Wallace, 2006; reviewed by Bateman et al., 2009). One of the many significant implications of this work is that most studies of any kind that purport to have involved Platanthera hyperborea may not in fact have done so; rather, most have investigated materials that originated from North America or, less frequently, northeast Asia and are therefore likely to represent segregates of P. hyperborea s.s. The holotype of ‘Orchis’ (later Platanthera) hyperborea bears the label “Oxeraa, Iceland, 1767.” We presume that this is a reference to the River Oxeraa, which runs through the historical capital of Iceland at Thingvellir in southwest Iceland (Fig. 1). Given that it was the first member of Section Limnorchis to be formally described, Icelandic P. hyperborea is inevitably pivotal in unravelling the systematics of the group. However, no Icelandic plants have yet been analysed in order to test some of the intriguing hypotheses that have emerged from the North American research, not least the possibility that the lineage migrated as airborne seed to Iceland eastward from North America (most likely via southern Greenland).


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

Bateman RM, Sramkó G, Rudall PJ - PeerJ (2015)

Populations of Platanthera hyperborea sampled in southwest Iceland during the present study.Base image also shows the capital Reykjavik, southwestern islands, icecaps and major rivers (courtesy of GoogleEarth). The dashed line in the inset denotes the Arctic Circle.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4400879&req=5

fig-1: Populations of Platanthera hyperborea sampled in southwest Iceland during the present study.Base image also shows the capital Reykjavik, southwestern islands, icecaps and major rivers (courtesy of GoogleEarth). The dashed line in the inset denotes the Arctic Circle.
Mentions: Initially, taxonomic discussions were driven entirely by perceived phenotypic complexity (cf. Luer, 1975; Sheviak, 2002; Delforge, 2006), but later became informed by the gradual accumulation of molecular systematic data across the genus (Hapeman & Inoue, 1997; Bateman et al., 2003; Bateman et al., 2009). More focused investigations of North American representatives of Section Limnorchis, most notably those pursued by Lisa Wallace, have revealed considerable genetic complexity, driven in part by allopolyploidy (Wallace, 2002; Wallace, 2003; Wallace, 2004; Wallace, 2006; reviewed by Bateman et al., 2009). One of the many significant implications of this work is that most studies of any kind that purport to have involved Platanthera hyperborea may not in fact have done so; rather, most have investigated materials that originated from North America or, less frequently, northeast Asia and are therefore likely to represent segregates of P. hyperborea s.s. The holotype of ‘Orchis’ (later Platanthera) hyperborea bears the label “Oxeraa, Iceland, 1767.” We presume that this is a reference to the River Oxeraa, which runs through the historical capital of Iceland at Thingvellir in southwest Iceland (Fig. 1). Given that it was the first member of Section Limnorchis to be formally described, Icelandic P. hyperborea is inevitably pivotal in unravelling the systematics of the group. However, no Icelandic plants have yet been analysed in order to test some of the intriguing hypotheses that have emerged from the North American research, not least the possibility that the lineage migrated as airborne seed to Iceland eastward from North America (most likely via southern Greenland).

Bottom Line: 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.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.When considered in combination with independently derived lineages of Platanthera on the Azorean and Hawaiian archipelagos also bearing small green flowers, our observations show allometric and paedomorphic reductions in flower size as the primary evolutionary driver, but also indicate strong developmental and functional constraints.

View Article: PubMed Central - HTML - PubMed

Affiliation: Royal Botanic Gardens Kew , Richmond , United Kingdom.

ABSTRACT
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 before passing through North America and presumably Greenland. The incohesive pollinia, rapidly desiccating anther locules, weakly developed rostellum, exceptionally adhesive stigma and the close juxtaposition of compact male and female reproductive organs together conspire to cause routine autogamy and frequent cleistogamy, despite the continued production of substantial nectar reservoirs in the spur and consequent ongoing attraction to the flowers of insects, including mosquitoes. When considered in combination with independently derived lineages of Platanthera on the Azorean and Hawaiian archipelagos also bearing small green flowers, our observations show allometric and paedomorphic reductions in flower size as the primary evolutionary driver, but also indicate strong developmental and functional constraints.

No MeSH data available.


Related in: MedlinePlus