British Moss Breaks Century of Celibacy

John Pickrell
for National Geographic News
January 23, 2003
A rare species of moss, found only in a few European locations, has
fruited for the first time in nearly 140 years.

Prior to last fall, when fruiting carpets of Nowell's moss were discovered in a rural area of northwest England, the species hadn't been known to reproduce sexually since 1866.

Scientists behind the discovery now believe that the unusually long celibacy may have been due to the fact that the rare plants were too far apart from one another to successfully mate.

"Locating the moss was very exciting. But even more so when I realized it hadn't been able to reproduce successfully all these years because the moss patches—which are either male or female, and mate via the spreading of spores—just haven't been close enough to reproduce," said Fred Rumsey, a biodiversity researcher at the Natural History Museum in London.

The researchers, who announced the finding earlier this month, plan to submit the discovery for publication in the Journal of Bryology sometime early this year.

Nowell's moss (Zygodon gracilis) is very rare and is only known from a few locations in the United Kingdom and historical records in the central European Alps. It was first discovered in 1860 by John Nowell an amateur Victorian botanist from whom the species takes its name. It was shortly after Nowell's discovery that the moss was seen to fruit for the last time.

Patches of Nowell's moss are usually one sex only. Still, the species doesn't have to rely on the opposite sex to reproduce, and most of the time propagates itself when chunks break off and continue to grow in a new location.

Chance Discovery

Rumsey and his botanist colleague Alistair Headley of the University of Bradford in West Yorkshire, England, set out on a mission last fall to document the remaining patches of the species in the undulating Yorkshire dales.

The pair located nearly 500 moss patches growing on just a few stretches of old stone wall in the scenic Pennine hills. But only one small patch was fruiting. The yellow-green, tufted moss was covered with tiny, cylindrical fruiting bodies on stalks, each packed with thousands of spores.

"In some places the patches [of Nowell's moss] are only a few meters apart," said Rumsey. "But this still seems to far for it to reproduce." Fruiting may have occurred in this instance because moss of one sex was somehow knocked or blown onto a patch of the opposite sex, said Rumsey.

Removal and renovation of old limestone walls in the area has accelerated the decline of Nowell's moss. It now exists on the few remaining walls that are several centuries old, Rumsey said.

The lack of sexual reproduction hasn't helped either—though mosses are able to persist through asexual means alone, the tiny, numerous spores produced in fruiting are needed to colonize new sites.

While all species of moss should be able to fruit, at least 10 percent of the 1,000 or more moss and liverwort species found in Britain have never been known to fruit there, said Rumsey. "In fact, some species are only known to have a single sex," he added.

Dangerous Liaison

For moss sperm, attempts at fertilizing the female of the species may be doomed before they even begin.

"Mosses…have a primitive fertilization system that involves sperm having to swim through liquid water from one plant to another," said Brent D. Mishler, a moss biologist and director of the Jepson Herbaria at the University of California, Berkeley. "Given that sperm have to swim, the sexes have to be [no more than] a few centimeters apart for fertilization to work," he said.

Unlike more-advanced land plants—such as pines and flowering plants—mosses haven't developed pollen. Pollen is used to carry a plant's male reproductive cells close to the female's egg cells before they are released.

Many species of moss have no known sex at all, said Mishler. As moss species have moved to drier habitats, over evolutionary time, there has been a trend to give up sex altogether, he said. Finding that sex still occurs in some species is important as it has implications for how the species should be conserved, he said.

"Something like 20 percent of British mosses are endangered," said Nick Hodgetts, a freelance moss biologist based in Lincolnshire, England, who formerly served on the Joint Nature Conservation Committee, a U.K. government conservation body. "The discovery of sexual reproduction is quite significant as it will greatly increase this species chance of survival," he said.

Rumsey and Headley now plan to attempt a little matchmaking by wedging small cushions of male moss next to female patches and vice versa.

The "discovery gives us a great opportunity to slow down, and possibly even halt, the extinction of a very interesting, but mostly overlooked species," said Rumsey.

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