Biologists have discovered that the water lily may be a critical 'missing link' in the evolution of flowering plants.

One of the great mysteries of evolutionary biology is how, 150 or more million years ago, modern-day angiosperms (flowering plants) diverged from their closest relatives, the gymnosperms (seed-bearing plants without flowers, such as pine trees with pine cones). A developmental study of the water lily, Nuphar polysepalum, may provide an important clue.

Joseph Williams and William Friedman of the University of Colorado report their National Science Foundation (NSF) supported findings in the January 31 issue of the journal Nature. This is a significant first-time discovery because now we are a big step closer to understanding the evolution of flowering plants, says Erik Nilsen, the NSF project officer.

An established and distinguishing feature of flowering plants is that each seed consists of two parts:

• 1) an embryo that is similar to that of all other plants, and
• 2) a unique tissue called the endosperm, which functions to nourish the embryo and which most people know as grain.

Virtually all angiosperms have endosperm that is triploid, that is, it contains three copies of each chromosome: two from the mother and one from the fathers sperm. This triploid endosperm contrasts dramatically with the seeds of gymnosperms, in which the nourishing tissue is haploid containing a single copy of each chromosome. The question of how endosperm originated, in an evolutionary sense, has perplexed biologists for over a century, states Friedman.

Williams and Friedman focused on the water lily family because fossil records and recent molecular analyses place it among the most ancient of flowering plants.

They measured DNA contents of embryo and endosperm cells using fluorescence microscopy to discover that the water lily has a diplo
'"/>

Contact: Andrea M. Dietrich
adietric@nsf.gov
703-292-8070
National Science Foundation
30-Jan-2002