AOBPreview originally published online on May 4, 2006
Annals of Botany 2006 98(1):123-140; doi:10.1093/aob/mcl078
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Former Diversity of Ephedra (Gnetales): Evidence from Early Cretaceous Seeds from Portugal and North America
1 Department of Palaeobotany, Swedish Museum of Natural History, Box 50007, S-104 05 Stockholm, Sweden, 2 Department of Botany, Stockholm University, S-106 91 Stockholm, Sweden, 3 Department of Geology, University of Aarhus, Universitetsparken, DK-8000 Århus C, Denmark and 4 Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, UK
* For correspondence. E-mail Catarina.Rydin{at}nrm.se
Received: 5 October 2005 Returned for revision: 22 December 2005 Accepted: 6 March 2006 Published electronically: 4 May 2006
• Background and Aims The extant species of the seed plant group Gnetales (Ephedra, Gnetum and Welwitschia) have been considered a remnant of a much greater, now extinct, diversity due to the pronounced differences in form and ecology among the genera. Until recently, this hypothesis has not been supported by evidence from the fossil record. This paper adds to the expanding information on Gnetales from the Early Cretaceous and describes coalified seeds from Barremian-Albian localities in Portugal and USA.
• Methods The fossils were extracted from sediment samples by sieving in water. Adhering mineral matrix was removed by chemical treatment. Seeds were investigated using light and scanning electron microscopy. Morphology and anatomy of the seeds were documented and compared with those of extant species.
• Key Results The fossils share characters with extant Ephedra, for example papillae on the inner surface of the seed envelope and in situ polyplicate pollen grains that shed the exine during germination. They differ from extant Ephedra seeds in morphological and anatomical details as well as in their smaller size. Two new species of Ephedra are described together with one species assigned to a new genus of Gnetales. Other Ephedra-like seeds, for which pollen and critical morphological details are currently unknown, are also present in the samples.
• Conclusions These Cretaceous seeds document that key reproductive characters and pollen germination processes have remained unchanged within Ephedra for about 120 million years or more. There is sufficient variety in details of morphology to suggest that a diversity of Ephedra and Ephedra-like species were present in the Early Cretaceous flora. Their presence in Portugal and eastern North America indicates that they were widespread on the Laurasian continent. The fossil seeds are similar to seeds of Erdtmanithecales and this supports the previously suggested relationship between Erdtmanithecales and Gnetales.
Key words: Early Cretaceous, Ephedra, Erdtmanispermum, Erdtmanithecales, Eucommiidites, fossil pollen, fossils, Gnetales, Portugal, Potomac Group, seeds