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

Portion of the preferred most-parsimonious ITS tree that encompasses Platanthera section Limnorchis, showing three well-supported species groups.Figures are bootstrap values and (in parentheses) decay indices.
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fig-4: Portion of the preferred most-parsimonious ITS tree that encompasses Platanthera section Limnorchis, showing three well-supported species groups.Figures are bootstrap values and (in parentheses) decay indices.

Mentions: The 46 ribotypes included in the aligned ITS matrix yielded 713 characters (including 58 scored indels), of which 197 (including 22 indels) proved phylogenetically informative. When analysed under amb- nodal collapse in PAUP, the matrix yielded 625 most-parsimonious trees of length 691 steps, Consistency Index of 0.645 (0.546 when excluding mutations unique to a single ribotype, i.e., autapomorphies sensu lato) and Retention Index of 0.826. Unsurprisingly, adding a further seven low-divergence ITS ribotypes for P. hyperborea and its close relatives did not alter the broad-brush topologies that we have generated during previous analyses of ITS data in Platanthera (Bateman et al., 2009; Bateman et al., 2014). Rather than reproduce the entire Platanthera phylogeny yet again, here we have chosen to illustrate only the relevant clade within the genus, Section Limnorchis (Fig. 4).


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)

Portion of the preferred most-parsimonious ITS tree that encompasses Platanthera section Limnorchis, showing three well-supported species groups.Figures are bootstrap values and (in parentheses) decay indices.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig-4: Portion of the preferred most-parsimonious ITS tree that encompasses Platanthera section Limnorchis, showing three well-supported species groups.Figures are bootstrap values and (in parentheses) decay indices.
Mentions: The 46 ribotypes included in the aligned ITS matrix yielded 713 characters (including 58 scored indels), of which 197 (including 22 indels) proved phylogenetically informative. When analysed under amb- nodal collapse in PAUP, the matrix yielded 625 most-parsimonious trees of length 691 steps, Consistency Index of 0.645 (0.546 when excluding mutations unique to a single ribotype, i.e., autapomorphies sensu lato) and Retention Index of 0.826. Unsurprisingly, adding a further seven low-divergence ITS ribotypes for P. hyperborea and its close relatives did not alter the broad-brush topologies that we have generated during previous analyses of ITS data in Platanthera (Bateman et al., 2009; Bateman et al., 2014). Rather than reproduce the entire Platanthera phylogeny yet again, here we have chosen to illustrate only the relevant clade within the genus, Section Limnorchis (Fig. 4).

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