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Double Fertilization in Ephedra, a Nonflowering Seed Plant: Its Bearing on the Origin of Angiosperms
William E. Friedman
New Series, Vol. 247, No. 4945 (Feb. 23, 1990), pp. 951-954
Published by: American Association for the Advancement of Science
Stable URL: http://www.jstor.org/stable/2873891
Page Count: 4
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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 phylogcnctic 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.
Science © 1990 American Association for the Advancement of Science