Who knew botany and mycology could be so naughty? Naked ladies and smut have come to light in the U.K., but not in the way you might think.

Yes, you can get your minds out of the gutter. We're talking about the rare plant called the naked ladies crocus (Colchicum autumnale) and the even rarer sooty-black smut fungus (Urocystis colchici). The fungus showed up this month on a single naked ladies crocus at Westonbirt Arboretum in Gloucestershire, England, which marked only the fourth time the critically endangered smutty fungus has been observed since 1938. (At least eight other varieties and forms of the fungus can be found around the world, including the U.S., where it affects onions, but the base species has only been observed in the U.K.)

The naked ladies crocus, which itself is listed as a "near threatened" species in the U.K., gets its name from its propensity to lose its spring leaves before the plant flowers in the autumn, leaving the buds "naked." The rotting spring leaves, meanwhile, are the only known host for the sooty-black smut fungus. (Smut fungi, by the way, get their name from the German word schmutz, meaning dirt, which they resemble. There are about 1,000 known species of smut fungi around the world.)

Dave Shorten of the Cotswold Fungus Group, who discovered this month's fungus, found it growing on a few leaves of a single plant within the 242-hectare park during one of the group's "fungus forays," in which the mycological enthusiasts spend their Sundays documenting the fungi of various parks in the Gloucestershire region. As you can see from the photo accompanying this article, the fungus does look like a small spot of dirt on the leaves of the crocus. According to the U.K. Forestry Commission, each cluster of fungus produces hundreds of thousands of brown-black spores, each 15 to 35 microns in diameter. (A micron is one millionth of a meter.)

This is actually the second sooty-black smut fungus sighting this year but just the 27th time it has ever been recorded in the U.K. The most recent sighting took place on May 10 about 80 kilometers away, in Oxfordshire. Mycologists also observed the fungus in 2002 and 2003 at Moccas Park in Herefordshire. Before that, the last sighting was in 1938.

Shorten says the way the Forestry Commission manages the arboretum makes the site a perfect habitat for a large variety of fungi. The arboretum's many paths are kept clear, but any wood or leaves that fall on the ground are left to decay naturally. Not only does this provide extra nutrients to the soil, it has also created a perfect breeding ground for birds, insects and fungi. Shorten says he and his predecessors have cataloged 1,271 fungi species at Westonbirt so far, and expects to identify still more in the coming months.

Because of its rarity, the smutty fungus is a legally protected species in the U.K. and is considered to be of "principal conservation importance." The Forestry Commission warns that it should not be picked and asks anyone else who observes it in the region to contact the Cotswold Fungus Group.

Photo: The sooty-black smut fungus (Urocystis colchici) on the leaves of a naked ladies crocus (Colchicum autumnale). Photo by Dave Shorten, courtesy of the U.K. Forestry Commission

Previously in Extinction Countdown: