Scientists have discovered that every plant species alive on land today shares a single common ancestor, at least 450 million years old.

The finding, by the 200 scientists of the Green Plant Phylogeny Research Co-ordination Group, was disclosed at the 1999 meeting of the International Botanical Congress in St Louis, Missouri, US.

The group, drawn from 12 countries, has spent five years reconstructing the evolutionary relationships among all of the Earth's green plants.

It says it has now developed the most complete "tree of life" of any group of living things.

Blurring the boundaries

One team member is Brent Mishler, professor of integrative biology at the University of California, Berkeley.

He said: "Better understanding of this 'tree of life' will allow scientists to better predict the biological properties of plants".

The team has clarified the plant "kingdoms" and their relationships to animals.

The tree of life reveals some surprises

They say there are five main trunks, or lineages, of complex, "nucleated" organisms on the Earth's genealogical tree, four of them classified as plants.

These are the green plants, the red ones (mostly seaweeds), the brown plants, and the fungi, which themselves revealed a surprise.

Professor Mishler said: "We can't really think of life on Earth in terms of only the 'animal kingdom' and the 'plant kingdom' any more".

"The fungi are more related to animals than to plants meaning that the mushrooms you eat are more related to you than to the tree on which they are growing."

The original seed

The group also says that the green conquest of the land was not led by seawater plants, but by freshwater ones, a reversal of traditional scientific understanding.

And they say that only one plant was responsible for the wealth of species alive today.

Every land plant alive today springs from a common stock

"Plants came out onto land probably many times, but only one lineage actually made it", said Professor Mishler.

"This indicates there's an Eve - a common ancestor - in the primordial soup of green plants."

The group's research shows as well that all the plants and animals together form only a small part of the mass of living things.

The rest of it consists of mostly single-celled and poorly-known organisms.

The researchers think the impact of this finding could parallel the discovery centuries ago that the Sun is merely one star in the whole universe.

They say their findings could shatter preconceptions about life on Earth by showing that all the familiar biodiversity (including human life) represents only one small twig on the tree of life.