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MBE Advance Access published online on March 5, 2003
Molecular Biology and Evolution, doi:10.1093/molbev/msg049
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2003; all rights reserved
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Accepted November 18, 2002
© 2003 Society for Molecular Biology and Evolution

Original Articles

Estimation of the Age of Extant Ephedra using Chloroplast RBCL Sequence Data

Jinling Huang 1* Robert A. Price 1

1 Department of Plant Biology, University of Georgia, Athens, GA 30602

* To whom correspondence should be addressed. E-mail: tupistra{at}yahoo.com.


  Abstract

The distinctive gymnosperm genus Ephedra is sometimes considered to have originated over 200 million years (Myr) ago on the basis of "ephedroid" fossil pollen. In this paper we estimate the age of extant Ephedra using chloroplast rbcL gene sequences. Relative rate tests fail to reject the null hypothesis of equal rates of nucleotide substitution of the rbcL sequences among three landmark lineages (Gnetales, Pinaceae, and Ginkgo biloba). The most divergent sequences we have found in Ephedra differ by only 7 bp for an 1110 bp region of rbcL sequence, while the differences among genera range from 92-107 bp in Gnetales and 35-92 bp in Pinaceae. Using three landmark events, the age of extant Ephedra is estimated to be approximately 8-32 Myr. Our result is consistent with the current distribution of many Ephedra species in geologically recent habitats and points out difficulties in the identification of older "ephedroid" pollen fossils with the modern genus Ephedra.

Key Words: time of origin, Ephedra, rate of nucleotide substitution, rbcL, molecular clock


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