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Osmunda pulchella sp. nov. from the Jurassic of Sweden--reconciling molecular and fossil evidence in the phylogeny of modern royal ferns (Osmundaceae).

Bomfleur B, Grimm GW, McLoughlin S - BMC Evol. Biol. (2015)

Bottom Line: Osmunda pulchella is likely a precursor of the Osmundastrum lineage.The recently proposed root placement in Osmundaceae-based solely on molecular data-stems from possibly misinformative outgroup signals in rbcL and atpA genes.We conclude that the seemingly conflicting evidence from morphological, anatomical, molecular, and palaeontological data can instead be elegantly reconciled under the assumption that Osmunda is indeed monophyletic.

View Article: PubMed Central - PubMed

Affiliation: Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden. benjamin.bomfleur@nrm.se.

ABSTRACT

Background: The classification of royal ferns (Osmundaceae) has long remained controversial. Recent molecular phylogenies indicate that Osmunda is paraphyletic and needs to be separated into Osmundastrum and Osmunda s.str. Here, however, we describe an exquisitely preserved Jurassic Osmunda rhizome (O. pulchella sp. nov.) that combines diagnostic features of both Osmundastrum and Osmunda, calling molecular evidence for paraphyly into question. We assembled a new morphological matrix based on rhizome anatomy, and used network analyses to establish phylogenetic relationships between fossil and extant members of modern Osmundaceae. We re-analysed the original molecular data to evaluate root-placement support. Finally, we integrated morphological and molecular data-sets using the evolutionary placement algorithm.

Results: Osmunda pulchella and five additional Jurassic rhizome species show anatomical character suites intermediate between Osmundastrum and Osmunda. Molecular evidence for paraphyly is ambiguous: a previously unrecognized signal from spacer sequences favours an alternative root placement that would resolve Osmunda s.l. as monophyletic. Our evolutionary placement analysis identifies fossil species as probable ancestral members of modern genera and subgenera, which accords with recent evidence from Bayesian dating.

Conclusions: Osmunda pulchella is likely a precursor of the Osmundastrum lineage. The recently proposed root placement in Osmundaceae-based solely on molecular data-stems from possibly misinformative outgroup signals in rbcL and atpA genes. We conclude that the seemingly conflicting evidence from morphological, anatomical, molecular, and palaeontological data can instead be elegantly reconciled under the assumption that Osmunda is indeed monophyletic.

Show MeSH
Details of petiole-base anatomy of Osmunda pulchella sp. nov. from the Lower Jurassic of Skåne, southern Sweden, revealed via scanning electron microscopy. a Distal cross-section through a petiole. b Detail of (a) showing vascular strand with about eight endarch protoxylem bundles and sclerenchyma mass lining the vascular-strand concavity. c Detail showing helical wall thickening of protoxylem strands (center) compared to multiseriate scalariform wall thickenings of metaxylem tracheids in a petiole vascular bundle (oriented with adaxial side facing upwards). Scale bars: (a) = 1 mm; (b) = 100 μm; (c) = 50 μm
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Fig6: Details of petiole-base anatomy of Osmunda pulchella sp. nov. from the Lower Jurassic of Skåne, southern Sweden, revealed via scanning electron microscopy. a Distal cross-section through a petiole. b Detail of (a) showing vascular strand with about eight endarch protoxylem bundles and sclerenchyma mass lining the vascular-strand concavity. c Detail showing helical wall thickening of protoxylem strands (center) compared to multiseriate scalariform wall thickenings of metaxylem tracheids in a petiole vascular bundle (oriented with adaxial side facing upwards). Scale bars: (a) = 1 mm; (b) = 100 μm; (c) = 50 μm

Mentions: In the inner cortex of the petiole, thick-walled fibres appear in the form of a small irregular mass adaxial to the vascular bundle (Fig. 5c, d). This mass develops distally into a thick band lining the bundle concavity (Figs. 5e, 6a, b), and may further differentiate into two lateral masses connected only by a rather thin strip (Fig. 5f, g). Apart from the sclerenchyma inside the vascular-bundle concavity, the inner cortex of the petiole consists entirely of parenchyma.Fig. 6


Osmunda pulchella sp. nov. from the Jurassic of Sweden--reconciling molecular and fossil evidence in the phylogeny of modern royal ferns (Osmundaceae).

Bomfleur B, Grimm GW, McLoughlin S - BMC Evol. Biol. (2015)

Details of petiole-base anatomy of Osmunda pulchella sp. nov. from the Lower Jurassic of Skåne, southern Sweden, revealed via scanning electron microscopy. a Distal cross-section through a petiole. b Detail of (a) showing vascular strand with about eight endarch protoxylem bundles and sclerenchyma mass lining the vascular-strand concavity. c Detail showing helical wall thickening of protoxylem strands (center) compared to multiseriate scalariform wall thickenings of metaxylem tracheids in a petiole vascular bundle (oriented with adaxial side facing upwards). Scale bars: (a) = 1 mm; (b) = 100 μm; (c) = 50 μm
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4487210&req=5

Fig6: Details of petiole-base anatomy of Osmunda pulchella sp. nov. from the Lower Jurassic of Skåne, southern Sweden, revealed via scanning electron microscopy. a Distal cross-section through a petiole. b Detail of (a) showing vascular strand with about eight endarch protoxylem bundles and sclerenchyma mass lining the vascular-strand concavity. c Detail showing helical wall thickening of protoxylem strands (center) compared to multiseriate scalariform wall thickenings of metaxylem tracheids in a petiole vascular bundle (oriented with adaxial side facing upwards). Scale bars: (a) = 1 mm; (b) = 100 μm; (c) = 50 μm
Mentions: In the inner cortex of the petiole, thick-walled fibres appear in the form of a small irregular mass adaxial to the vascular bundle (Fig. 5c, d). This mass develops distally into a thick band lining the bundle concavity (Figs. 5e, 6a, b), and may further differentiate into two lateral masses connected only by a rather thin strip (Fig. 5f, g). Apart from the sclerenchyma inside the vascular-bundle concavity, the inner cortex of the petiole consists entirely of parenchyma.Fig. 6

Bottom Line: Osmunda pulchella is likely a precursor of the Osmundastrum lineage.The recently proposed root placement in Osmundaceae-based solely on molecular data-stems from possibly misinformative outgroup signals in rbcL and atpA genes.We conclude that the seemingly conflicting evidence from morphological, anatomical, molecular, and palaeontological data can instead be elegantly reconciled under the assumption that Osmunda is indeed monophyletic.

View Article: PubMed Central - PubMed

Affiliation: Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden. benjamin.bomfleur@nrm.se.

ABSTRACT

Background: The classification of royal ferns (Osmundaceae) has long remained controversial. Recent molecular phylogenies indicate that Osmunda is paraphyletic and needs to be separated into Osmundastrum and Osmunda s.str. Here, however, we describe an exquisitely preserved Jurassic Osmunda rhizome (O. pulchella sp. nov.) that combines diagnostic features of both Osmundastrum and Osmunda, calling molecular evidence for paraphyly into question. We assembled a new morphological matrix based on rhizome anatomy, and used network analyses to establish phylogenetic relationships between fossil and extant members of modern Osmundaceae. We re-analysed the original molecular data to evaluate root-placement support. Finally, we integrated morphological and molecular data-sets using the evolutionary placement algorithm.

Results: Osmunda pulchella and five additional Jurassic rhizome species show anatomical character suites intermediate between Osmundastrum and Osmunda. Molecular evidence for paraphyly is ambiguous: a previously unrecognized signal from spacer sequences favours an alternative root placement that would resolve Osmunda s.l. as monophyletic. Our evolutionary placement analysis identifies fossil species as probable ancestral members of modern genera and subgenera, which accords with recent evidence from Bayesian dating.

Conclusions: Osmunda pulchella is likely a precursor of the Osmundastrum lineage. The recently proposed root placement in Osmundaceae-based solely on molecular data-stems from possibly misinformative outgroup signals in rbcL and atpA genes. We conclude that the seemingly conflicting evidence from morphological, anatomical, molecular, and palaeontological data can instead be elegantly reconciled under the assumption that Osmunda is indeed monophyletic.

Show MeSH