Add 1--Plant evolution

A tiny organism, about the size of a period, Coleochaete is found in
clean, fresh water throughout the world. And of any living alga, it exhibits
the greatest similarity to land plants.
"We know that there is a relatively small group of organisms from which
land plants could have derived," said Delwiche. "A big question was what was
it about the ancestors of land plants that allowed them to survive and succeed
on land?"
The findings of the Wisconsin group raise questions about the dominant
role of lignin-like materials. Such materials have long been recognized as
having two critical functions: providing structural support for plants and
useful antimicrobial properties.
It has long been thought that the antimicrobial properties of lignin-like
materials arose secondary to their structural characteristics.
But the Wisconsin research suggests that lignin-like materials evolved
prior to the separation of land plants, with their requirement for the rigid
properties of lignin-like materials, and their algal ancestors.
Lignin-like materials, explained Thomson, are biopolymers having molecular
structures made up of many different subunits. When the subunits are linked
together, he said, they form a rigid and durable barrier that microbes are
unable to penetrate.
"That rigidity was fortuitous," said Delwiche. "When algae began to
survive or. land, that property then became important in the development of
plants."
Although there are some species of modern algae known to colonize land,
mostly in damp or muddy environments but also in such curious places as sloth
fur, it is generally agreed upon by scientists that these were independent
colonizations of the land.
"There are species of algae that colonize land," Delwiche said, "but
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