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Pollen morphology of Ephedra (Gnetales) and its evolutionary implications
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Imperial College London, UK.
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Number of Authors: 7
2016 (English)In: Grana, ISSN 0017-3134, E-ISSN 1651-2049, Vol. 55, no 1, 24-51 p.Article in journal (Refereed) Published
Abstract [en]

The Ephedra lineage can be traced at least to the Early Cretaceous. Its characteristically polyplicate pollen is well-represented in the fossil record and is frequently used as an indicator of paleoclimate. However, despite previous efforts, knowledge about variation and evolution of ephedroid pollen traits is poor. Here, we document pollen morphology of nearly all extant species of Ephedra, using a combination of scanning electron microscopy (SEM) and light microscopy (LM), and reconstruct ancestral states of key pollen traits. Our results indicate that the ancestral Ephedra pollen type has numerous plicae interspaced by unbranched pseudosulci, while the derived pollen type has branched pseudosulci and (generally) fewer plicae. The derived type is inferred to have evolved independently twice, once along the North American stem branch and once along the Asian stem branch. Pollen of the ancestral type is common in Mesozoic fossil records, especially from the Early Cretaceous, but it is less commonly reported from the Cenozoic. The earliest documentation of the derived pollen type is from the latest Cretaceous, after which it increases strongly in abundance during the Paleogene. The results of the present study have implications for the age of crown group Ephedra as well as for understanding evolution of pollination syndromes in the genus.

Place, publisher, year, edition, pages
2016. Vol. 55, no 1, 24-51 p.
Keyword [en]
character evolution, light microscopy, phylogeny, polyplicate, pseudosulci, scanning electron microscopy, Welwitschia
National Category
Biological Sciences
Research subject
Plant Systematics
Identifiers
URN: urn:nbn:se:su:diva-129089DOI: 10.1080/00173134.2015.1066424ISI: 000371864800004OAI: oai:DiVA.org:su-129089DiVA: diva2:922461
Available from: 2016-04-22 Created: 2016-04-14 Last updated: 2017-03-28Bibliographically approved
In thesis
1. Pollen and pollination in Ephedra (Gnetales)
Open this publication in new window or tab >>Pollen and pollination in Ephedra (Gnetales)
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ephedra (Gnetales) is a gymnosperm genus with a long evolutionary history; the first dispersed pollen grains with affinity to the group are known already from the Permian. This thesis focuses on the evolutionary history of the group and different aspects of its pollination mechanisms. Despite the limited number of extant species of the genus (50-60), and a low morphological and genetic divergence among species, there is variation in pollination syndrome in the genus. The prevailing state in Ephedra, and most gymnosperms, is wind pollination. It is therefore surprising that one species, E. foeminea, is insect-pollinated. Together with co-workers I documented the pollination syndromes of E. foeminea and a sympatric species, E. distachya, based on long term field experiments in north-eastern Greece and aerodynamic investigations and calculations. Placing the results into an evolutionary framework reveals that the insect-pollinated species E. foeminea is sister to the remaining (mostly wind-pollinated) genus, and indicates that insect pollination is the ancestral state in the Gnetales. During the course of evolution of the group there has been a shift to wind pollination, which may have played a crucial role for the diversification of the crown group in the Paleogene. Pollination biology is often correlated with the morphology of the pollen such that pollen grains of anemophilous plants are small with a smooth surface, whereas pollen grains of entomophilous plants are larger with an ornamented surface and a covering of pollenkitt. The pollen morphology of Ephedra can be broadly divided into two types: an ancestral type with an unbranched pseudosulcus between each pair of plicae, and a derived type with a branched pseudosulcus between each pair of plicae. Further, the pollen morphology and ultrastructure of the pollen wall in Ephedra are to some degree correlated with the pollination syndrome and capability of long distance dispersal. Pollen of E. foeminea has a denser ultrastructure, as a result a higher settling velocity and is therefore capable of flying shorter distances than does pollen of the anemophilous E. distachya, and other investigated anemophilous species that show a more spacious ultrastructure of the pollen grain. These results can be useful in the reconstruction of the pollination mechanism of extinct taxa of the Ephedra-lineage in the future.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2017. 46 p.
Keyword
aerodynamics, evolution, moonlight, pollination, pollen morphology, ultrastructure
National Category
Evolutionary Biology Botany
Research subject
Plant Systematics
Identifiers
urn:nbn:se:su:diva-140771 (URN)978-91-7649-774-6 (ISBN)978-91-7649-775-3 (ISBN)
Public defence
2017-05-19, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
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Available from: 2017-04-26 Created: 2017-03-16 Last updated: 2017-04-03Bibliographically approved

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