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Science 23 February 1990:
Vol. 247. no. 4945, pp. 951 - 954
DOI: 10.1126/science.247.4945.951
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Articles

Double Fertilization in Ephedra, a Nonflowering Seed Plant: Its Bearing on the Origin of Angiosperms

William E. Friedman 1

1 Department of Botany, University of Georgia, Athens, GA 30602

Double fertilization and the associated formation of endosperm have long been considered unique and defining characters (autapomorphies) of the angiosperms. During normal fertilization in Ephedra nevadensis, a nonflowering seed plant, fusion of a second sperm nucleus with the ventral canal nucleus occurs regularly within the egg cytoplasm. The occurrence of double fertilization in Ephedra assumes added significance in light of its critical phylogenetic position as a basal member of the most closely related extant group of seed plants (Gnetales) to angiosperms. Thus, double fertilization in angiosperms and Ephedra may represent an evolutionary homology.

Submitted on October 2, 1989
Accepted on December 7, 1989


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