mirrored file at http://SaturnianCosmology.Org/ 
For complete access to all the files of this collection
	see http://SaturnianCosmology.org/search.php 
==========================================================

Harvard University Gazette

HARVARD GAZETTE ARCHIVES

Oldest Known Flowering Plants Identified By Genes

By William J. Cromie 
Gazette Staff

The water lily's origins go back more than 140 million years. Photo by
Michael Donoghue.

It's a nondescript shrub with small, unimpressive flowers, and it's
found in only one place in the world - New Caledonia, a minor tropical
island in a remote corner of the southwest Pacific. But it has
suddenly catapulted to botanical eminence as a key piece in the puzzle
of the origins of flowering plants.
Called Amborella, the plant is the one remaining species of a lineage
that first appeared on Earth more than 140 million years ago, while
dinosaurs still ruled the planet. The other flowering plants, from
which it branched, evolved and diversified until they came to dominate
Earth at about the same time as the mammalian ancestors of humans were
replacing dinosaurs. Flowering plants now number 250,000 different
species, including virtually all the vegetables and grains we eat, as
well as most of the food of the animals that we consume. "It's
difficult to imagine a world without flowering plants," says Michael
Donoghue, professor of biology at Harvard University. As a result of
analyzing the genes from all flowering plants suspected of being among
the world's oldest, Donoghue and research associate Sarah Mathews
concluded that
Amborella and water lilies are the first two branches on the family
tree of flowering plants.

Michael Donoghue (right) and Sarah Mathews examine a Herbaria sample
of Amborella, which their research has identified as the oldest known
flowering plant. Photo by Justin Ide.

Mathews and Donoghue's analysis revealed that another early branch
includes Austrobaileya, a group represented by one species found only
in Australia, and by the more common star anise, which boasts bright
red, saucer-shaped flowers. Tracing flowering plants back so close to
their roots ranks as one of the major botanical discoveries of this
century. "We knew Amborella was a possible candidate, but to actually
pin it down after decades of speculation was a cause for great
excitement," Donoghue says. "One of the wonderful things is that three
other teams of scientists have come up with the same result." The
other scientists did different types of genetic analyses at
universities in the United States, Canada, and Switzerland. Mathews
and Donoghue published their results first, in the Oct. 29 issue of
the U.S. journal Science. Two other teams published their findings in
the Nov. 25 issue of the British journal Nature.Flowers on the Tree of
Life Despite these new findings, plenty of mysteries remain. None of
the analyses reveals when the first flowering plant appeared on Earth.
Amborella is not the first one but, rather, a representative of the
first branch from that unknown ancestor. Sometime before 140 million
years ago, flowering plants, known as angiosperms, diverged from
nonflowering seed plants known as gymnosperms. Biologists imagine a
tree of life with different groups of animals or plants as branches.
Flowering plants branched off from within the branch of seed plants.
The first branch within flowering plants separated Amborella from all
the rest. Fossils of gymnosperms, such as pine trees and other
evergreens, go back at least 350 million years, when cockroaches as
big as house cats and dragonflies with the wingspans of modern hawks
prowled the planet. Therefore, the birth of flowering plants could
have occurred anytime between 140 million and 350 million years ago.
Botanists would like to narrow that gap. Another mystery involves how
flowering plants were able to diversify so much and spread so rapidly.
Donoghue and Mathews see similarities in this expansion with that of
mammals after dinosaurs became extinct about 60 million years ago. The
key, they believe, lies in newly evolved structures not available to
nonflowering plants. One of these is the carpel, a womb-like vessel
that encloses the seeds of flowering plants. The word "angiosperm"
means "seed born in a vessel." "Gymnosperm" means "naked seed," a
reference to the lack of a protective structure enveloping the
developing seed. In modern plants, a leaflike carpel folds over one or
more seeds and its edges fuse together. The young plant develops
inside the seed with the help of a placenta-like nutritive tissue
known as the endosperm. Amborella, water lilies, and the star anise
have folded carpels, but they do not fuse shut. Instead, they secrete
a fluid that sticks the carpel edges shut. That doesn't sound like
much difference, but it gives botanists a rare glimpse of a modern
structure as it appeared more than 140 million years ago. "This is
probably how the carpel looked in the distant ancestors of flowering
plants," Donoghue says. "It's a neat observation that increases our
understanding of how flowering plants originated and what the first
ones looked like." The carpel probably helped flowering plants
disperse their seeds around the Earth. Undoubtedly, other features
evolved and gave certain lineages advantages that allowed them to
adapt to many environmental niches closed to gymnosperms. Today, the
latter are limited to about 750 species compared with 250,000
angiosperms. Mathews and Donoghue speculate that this glory road to
diversification and expansion contained many ruts of extinction.
Lineages of larger, woody, flowering plants are thought to have given
rise to smaller, herbaceous plants. Continued evolution of these less
woody species eventually made possible farming and the rise of modern
civilizations. It's something to think about the next time you look at
a water lily.

________________________________________________________

Copyright 1999 President and Fellows of Harvard College