By Matt Walker
Editor, Earth News
The plant that conquered: the peat moss Sphagnum subnitens
It is the most extreme example yet known of a single plant's ability to colonise sites spanning a huge region.
Across northwestern North America, every example of a common peat moss called Sphagnum subnitens is genetically identical, researchers have discovered.
That means every specimen can be traced back to a single parent, which likely conquered North America in less than 300 years, and shows how a single 'general purpose' genome can allow a plant to grow in a range of climates.
As part of the same research, scientists also discovered that just two parent peat moss plants of the same species have also produced all those now living in New Zealand.
It can be argued that this is the most genetically uniform widespread group of plants known
Plant ecologist Eric Karlin, Ramapo College in New Jersey, US
Both results are "extremely surprising", say the plant ecologists who did the research.
One reason is because the same is not true in Europe, where a wide variety of S. subnitens mosses live.
Details of the discovery are published in the journal Molecular Ecology.
Professor Eric Karlin of Ramapo College in New Jersey, US and colleagues at Binghamton University in New York state, US and Duke University, in Durham, North Carolina, US were initially studying the global distribution of S. subnitens.
"Like other peat mosses, the plant grows in bogs and fens," Prof Karlin told BBC News.
Standing just a few centimetres tall, the plant forms carpets and can vary in colour from green to red to brown.
"It is not uncommon," says Prof Karlin, but it does have an odd distribution, occurring widely in Europe and across coastal northwestern North America, and again in New Zealand, where it is limited to the west coast of the South Island.
"Prior to this study there had been no analysis to assess the genetic relationships of the plants in these remarkably disjunct populations," he adds.
A red form of the moss species
So he and colleagues did just that, also measuring the amount of genetic variety within populations of the peat moss growing on each continent.
"All of the plants of S. subnitens in northwestern North America appear to have descended from just one parent," says Prof Karlin.
"100% of the gene pool was contributed by one individual."
Genetically identical plants of S. subnitens range from coastal Oregon to the western Aleutian Islands, a distance of some 4115km.
In New Zealand, the populations there were founded by two different parents. But interestingly, these do not appear to have interbred.
"Thus all plants of S. subnitens in New Zealand are genetic copies of either one or the other founding parent."
The peat moss appears able to colonise many sites across extensive geographic regions due to its complicated way of reproducing.
Mosses can reproduce in a number of ways.
Either a moss plant clones itself, by passing on exactly the same DNA to new individuals via vegetative reproduction.
Or it can reproduce by sexual reproduction.
In humans and most animals, this usually occurs with a male parent providing the sperm and the female parent the egg, each supplying half their offspring's genetic material.
Peat mosses can do this, but they can also sexually reproduce another way, with the same parent producing both the sperm and egg.
This sperm and egg are also genetically different to each other, due to the way genetic material gets shifted around when they are created.
S. subnitens also has a fourth way of reproducing, however.
One parent can produce egg and sperm that are genetically identical.
When these sperm and eggs come together, they produce offspring containing two copies of identical DNA.
That means the offspring are genetically the same as their parent, without technically being clones.
This special type of sexual reproduction only occurs in some mosses and some other seedless plants such as ferns.
That is what Prof Karlin's team believes has happened in North America and New Zealand.
A single founder plant arrived in North America from Europe, probably sometime between the turn of the 18th and 20th Centuries.
It then reproduced, spreading genetically identical copies of itself along the northwestern coast.
"It can be argued that this is the most genetically uniform widespread group of plants known," says Prof Karlin.
Two different plants of this species must have arrived in New Zealand, and individually spread in the same way.
In neither North America, nor New Zealand, do any of the plants of S. subnitens show signs of genetic variation from the founding parents.
The apparent health of the peat moss populations indicates that the plant has not suffered from having no diversity in its genetic make up.
Prof Karlin explains: "This is in sharp contrast to many animals and plants." For them, inbreeding often leads to a concentration of unwanted genetic mutations, compromising their evolutionary fitness, he says.
But this peat moss shows how many ecological niches can be filled by just a single genome, albeit one copied many times.
"It appears that the species has a 'general purpose' genotype that can thrive without specialisation to each location where it occurs," says Prof Karlin.