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MBE Advance Access originally published online on March 5, 2003
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Mol. Biol. Evol. 20(3):435-440. 2003
DOI: 10.1093/molbev/msg049
© 2003 by the Society for Molecular Biology and Evolution. ISSN: 0737-4038

Estimation of the Age of Extant Ephedra Using Chloroplast rbcL Sequence Data

Jinling Huang1 and Robert A. Price

Department of Plant Biology, University of Georgia, Athens, Georgia

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 article 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). The most divergent sequences we have found in Ephedra differ by only 7 bp for an 1,110 bp region of rbcL sequence, whereas the differences among genera range from 92 to 107 bp in Gnetales and from 35 to 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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