A Christchurch homeowner has discovered that his abandoned home has been colonised by mushrooms. The mushrooms were growing on carpet which had become sodden and coated in silt from liquefaction that happened during the February earthquake in Christchurch.
My first encounter with this type of mushroom was as a new botany lecturer at the University of Otago when a student brought in a number of large flabby yellowish masses for me to identify. He had found them growing on the carpet behind a couch in his living room. A quick look under the microscope showed that it had the typical spores of an Ascomycete fungus. At that time the only quick guide to fungi in New Zealand was Marie Taylor’s little book of mushrooms and toadstools. From this, I identify it, somewhat tentatively, as Peziza vesiculosa (the fawn cup). According to Marie the fawn cup grows damp cardboard and sacking left lying on the ground which is similar enough to damp carpet. I was able to confirm this attraction to decomposing waste a few years later when I mulched my garden with a thick layer of newspaper covered by woodchip which then produced a magnificent crop of fawn cups.
However, digging a bit deeper I came across closely related fungus Peziza domiciliana, the carpet cup, growing on damp carpet in California. It would appear to be a common household fungus around the world. According to a US air quality testing laboratory the carpet cup has been found growing in a wide range of building and household materials including plaster, cement, sand, coal dust, wet rugs and carpets, fireplace ashes, and walls. It has been found in a wide range of locations, including carpets in living rooms, shower stalls, damp closets, behind refrigerators, around leaky water beds, in cellars, greenhouses, under porches, walls in school rooms, and in cars.
With fungi the next question is always – is it poisonous? Most of the books say that the carpet cup is inedible and the same US lab says that it is believed to be non-toxic. In other words, no one has eaten it so we do not know if it is poisonous.
Well then if not poisonous could it cause allergic reactions to people exposed to it. The carpet caps seen in the photo are only the fruitbody that is like the apple on an apple tree. The ‘tree’ of the fungus consists of microscopic threads or hyphae that grow through the material the fungus is decomposing – in this case, carpet. The most obvious example of hyphae that people can see is the mould on bread and the mildew on curtains. Many of the fungi that cause moulds in our houses also produce other types of spores that do not require a fruit body. It is often these other types of spores that cause allergenic reactions. The phase of the fungal life cycle that produces these spores can often have a different name, just to be confusing to the outsider, and in this case it is Chromelosporium. The allergenicity of Chromelosporium spores of the carpet cup has not been studied so it is not known.