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Eobowenia gen. nov. from the Early Cretaceous of Patagonia: indication for an early divergence of Bowenia ?

View Article: PubMed Central - PubMed

ABSTRACT

Background: Even if they are considered the quintessential “living fossils”, the fossil record of the extant genera of the Cycadales is quite poor, and only extends as far back as the Cenozoic. This lack of data represents a huge hindrance for the reconstruction of the recent history of this important group. Among extant genera, Bowenia (or cuticles resembling those of extant Bowenia) has been recorded in sediments from the Late Cretaceous and the Eocene of Australia, but its phylogenetic placement and the inference from molecular dating still imply a long ghost lineage for this genus.

Results: We re-examine the fossil foliage Almargemia incrassata from the Lower Cretaceous Anfiteatro de Ticó Formation in Patagonia, Argentina, in the light of a comparative cuticular analysis of extant Zamiaceae. We identify important differences with the other member of the genus, viz. A. dentata, and bring to light some interesting characters shared exclusively between A. incrassata and extant Bowenia. We interpret our results to necessitate the erection of the new genus Eobowenia to accommodate the fossil leaf earlier assigned as Almargemia incrassata. We then perfom phylogenetic analyses, including the first combined morphological and molecular analysis of the Cycadales, that indicate that the newly erected genus could be related to extant Bowenia.

Conclusion: Eobowenia incrassata could represent an important clue for the understanding of evolution and biogeography of the extant genus Bowenia, as the presence of Eobowenia in Patagonia is yet another piece of the biogeographic puzzle that links southern South America with Australasia.

Electronic supplementary material: The online version of this article (doi:10.1186/s12862-017-0943-x) contains supplementary material, which is available to authorized users.

No MeSH data available.


Comparison between the cuticle of Eobowenia incrassata (a, c, e, specimen v52265) and Bowenia spectabilis (b, d, f). a Stomata on the abaxial cuticle of Eobowenia incrassata, showing the monocyclic architecture and the darker-staining pavement cells. The thickenings of the substomatal complexes are preserved under some stomata. b Stomata on the abaxial cuticle of Bowenia spectabilis, showing similar monocyclic stomatal architecture and the darker-staining (thickly cutinised) pavement cells. c Detail of two stomatal complexes in Eobowenia incrassata. The distal thickening (blue arrow) and the marginal ridge (white arrow) are clearly shown. d Detail of the stomatal complex in Bowenia spectabilis. Distal thickening (blue arrow) and the marginal ridge (white arrow) are present in the cuticle of the guard cells. e Detail of a stomatal complex in Eobowenia incrassata showing the partially preserved substomatal complex with secondary thickenings (black arrow). f The substomatal complex shown in a confocal stack of PI-stained leaflets of Bowenia spectabilis. Thickenings are indicated by the black arrow. b and d are light micrographs (b) or fluorescence pictures (d) of the cleared cuticle of Bowenia spectabilis. Scale bars: 50 μm
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Fig3: Comparison between the cuticle of Eobowenia incrassata (a, c, e, specimen v52265) and Bowenia spectabilis (b, d, f). a Stomata on the abaxial cuticle of Eobowenia incrassata, showing the monocyclic architecture and the darker-staining pavement cells. The thickenings of the substomatal complexes are preserved under some stomata. b Stomata on the abaxial cuticle of Bowenia spectabilis, showing similar monocyclic stomatal architecture and the darker-staining (thickly cutinised) pavement cells. c Detail of two stomatal complexes in Eobowenia incrassata. The distal thickening (blue arrow) and the marginal ridge (white arrow) are clearly shown. d Detail of the stomatal complex in Bowenia spectabilis. Distal thickening (blue arrow) and the marginal ridge (white arrow) are present in the cuticle of the guard cells. e Detail of a stomatal complex in Eobowenia incrassata showing the partially preserved substomatal complex with secondary thickenings (black arrow). f The substomatal complex shown in a confocal stack of PI-stained leaflets of Bowenia spectabilis. Thickenings are indicated by the black arrow. b and d are light micrographs (b) or fluorescence pictures (d) of the cleared cuticle of Bowenia spectabilis. Scale bars: 50 μm

Mentions: The cuticle fragments examined show that the leaflets are hypostomatic with epidermal pavement cells longitudinally elongated parallel to the leaflet axis (Fig. 2 c, d). Ordinary epidermal cells are elongate and moderately cutinised. On the adaxial side, rows of cells with thicker cuticle than the ordinary pavement cells can be observed (darker staining; equivalent to the thin-walled cells of most Zamiaceae (see [54])), which seem to be arranged preferably in rows of short cells. The anticlinal walls of these dark-staining cells tend to be slightly concave. On the abaxial side, rows of darker staining cells as well as single darker staining cells are present. The stomata are confined to the abaxial side and are distributed uniformly in broad intercostal bands on the leaflet surface, with the guard cells oriented longitudinally (Fig. 3a, c). Guard cells are in average 38.63 (35.53–42.30) μm long and 17.90 (16.86–19.71) μm wide, with an aperture that is 20.89 (14.78–23.98) μm long. The stomatal complexes are monocyclic, with four to six subsidiary cells that have a thicker, darker staining cuticle than the ordinary pavement cells. The cuticle of the guard cells presents a ventral thickening in the correspondence of the aperture as well as ridges that run parallel to the dorsal wall (Fig. 2 d; Fig. 3 c, e; Fig. 4 a). In some stomatal complexes, is possible to observe differentially thickened or perforated cell walls, which are similar to the cell wall of the substomatal complex in extant Bowenia (Fig. 2 d; Fig. 3 e).Fig. 3


Eobowenia gen. nov. from the Early Cretaceous of Patagonia: indication for an early divergence of Bowenia ?
Comparison between the cuticle of Eobowenia incrassata (a, c, e, specimen v52265) and Bowenia spectabilis (b, d, f). a Stomata on the abaxial cuticle of Eobowenia incrassata, showing the monocyclic architecture and the darker-staining pavement cells. The thickenings of the substomatal complexes are preserved under some stomata. b Stomata on the abaxial cuticle of Bowenia spectabilis, showing similar monocyclic stomatal architecture and the darker-staining (thickly cutinised) pavement cells. c Detail of two stomatal complexes in Eobowenia incrassata. The distal thickening (blue arrow) and the marginal ridge (white arrow) are clearly shown. d Detail of the stomatal complex in Bowenia spectabilis. Distal thickening (blue arrow) and the marginal ridge (white arrow) are present in the cuticle of the guard cells. e Detail of a stomatal complex in Eobowenia incrassata showing the partially preserved substomatal complex with secondary thickenings (black arrow). f The substomatal complex shown in a confocal stack of PI-stained leaflets of Bowenia spectabilis. Thickenings are indicated by the black arrow. b and d are light micrographs (b) or fluorescence pictures (d) of the cleared cuticle of Bowenia spectabilis. Scale bars: 50 μm
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5383990&req=5

Fig3: Comparison between the cuticle of Eobowenia incrassata (a, c, e, specimen v52265) and Bowenia spectabilis (b, d, f). a Stomata on the abaxial cuticle of Eobowenia incrassata, showing the monocyclic architecture and the darker-staining pavement cells. The thickenings of the substomatal complexes are preserved under some stomata. b Stomata on the abaxial cuticle of Bowenia spectabilis, showing similar monocyclic stomatal architecture and the darker-staining (thickly cutinised) pavement cells. c Detail of two stomatal complexes in Eobowenia incrassata. The distal thickening (blue arrow) and the marginal ridge (white arrow) are clearly shown. d Detail of the stomatal complex in Bowenia spectabilis. Distal thickening (blue arrow) and the marginal ridge (white arrow) are present in the cuticle of the guard cells. e Detail of a stomatal complex in Eobowenia incrassata showing the partially preserved substomatal complex with secondary thickenings (black arrow). f The substomatal complex shown in a confocal stack of PI-stained leaflets of Bowenia spectabilis. Thickenings are indicated by the black arrow. b and d are light micrographs (b) or fluorescence pictures (d) of the cleared cuticle of Bowenia spectabilis. Scale bars: 50 μm
Mentions: The cuticle fragments examined show that the leaflets are hypostomatic with epidermal pavement cells longitudinally elongated parallel to the leaflet axis (Fig. 2 c, d). Ordinary epidermal cells are elongate and moderately cutinised. On the adaxial side, rows of cells with thicker cuticle than the ordinary pavement cells can be observed (darker staining; equivalent to the thin-walled cells of most Zamiaceae (see [54])), which seem to be arranged preferably in rows of short cells. The anticlinal walls of these dark-staining cells tend to be slightly concave. On the abaxial side, rows of darker staining cells as well as single darker staining cells are present. The stomata are confined to the abaxial side and are distributed uniformly in broad intercostal bands on the leaflet surface, with the guard cells oriented longitudinally (Fig. 3a, c). Guard cells are in average 38.63 (35.53–42.30) μm long and 17.90 (16.86–19.71) μm wide, with an aperture that is 20.89 (14.78–23.98) μm long. The stomatal complexes are monocyclic, with four to six subsidiary cells that have a thicker, darker staining cuticle than the ordinary pavement cells. The cuticle of the guard cells presents a ventral thickening in the correspondence of the aperture as well as ridges that run parallel to the dorsal wall (Fig. 2 d; Fig. 3 c, e; Fig. 4 a). In some stomatal complexes, is possible to observe differentially thickened or perforated cell walls, which are similar to the cell wall of the substomatal complex in extant Bowenia (Fig. 2 d; Fig. 3 e).Fig. 3

View Article: PubMed Central - PubMed

ABSTRACT

Background: Even if they are considered the quintessential “living fossils”, the fossil record of the extant genera of the Cycadales is quite poor, and only extends as far back as the Cenozoic. This lack of data represents a huge hindrance for the reconstruction of the recent history of this important group. Among extant genera, Bowenia (or cuticles resembling those of extant Bowenia) has been recorded in sediments from the Late Cretaceous and the Eocene of Australia, but its phylogenetic placement and the inference from molecular dating still imply a long ghost lineage for this genus.

Results: We re-examine the fossil foliage Almargemia incrassata from the Lower Cretaceous Anfiteatro de Ticó Formation in Patagonia, Argentina, in the light of a comparative cuticular analysis of extant Zamiaceae. We identify important differences with the other member of the genus, viz. A. dentata, and bring to light some interesting characters shared exclusively between A. incrassata and extant Bowenia. We interpret our results to necessitate the erection of the new genus Eobowenia to accommodate the fossil leaf earlier assigned as Almargemia incrassata. We then perfom phylogenetic analyses, including the first combined morphological and molecular analysis of the Cycadales, that indicate that the newly erected genus could be related to extant Bowenia.

Conclusion: Eobowenia incrassata could represent an important clue for the understanding of evolution and biogeography of the extant genus Bowenia, as the presence of Eobowenia in Patagonia is yet another piece of the biogeographic puzzle that links southern South America with Australasia.

Electronic supplementary material: The online version of this article (doi:10.1186/s12862-017-0943-x) contains supplementary material, which is available to authorized users.

No MeSH data available.