Unusual toadstool identified
Otago Museum
FOUR years ago a man from Norwood St, Dunedin, brought in 10 very hard objects for identification. These seemingly organic globular objects were 1724mm across, all with a wrinkled surface. They had been in the soil around his house for over five decades. I had never seen them before, nor had anyone to whom I showed them. They look somewhat like exceptionally hard unopened Monterey cypress (Cupressus
macrocarpa) seed pods. I had difficulty cutting them open, even with a chisel. The exposed interior looked possibly fungoid.
An Auckland mycologist had not seen these before, and used DNA extraction and sequencing to determine the species. It was, as she described, ‘‘really an unusual sample’’. She identified the nodules as sclerotia of the northernhemisphere toadstool
Agrocybe arvalis, which had not previously been found in New Zealand. It is a saprobe (living on decaying matter) and is commonly found growing on mulch in gardens in Europe and North America. This toadstool is one of the very few that forms a sclerotium which germinates directly into a toadstool.
A sclerotium is the resting or dormant stage of some fungi. During this stage, it becomes a mass of hardened or mummified tissue, usually a mass of hyphae, generally with no spores in it or on it. Ergot, a hard black tiny object on an ear of grain, is a sclerotium of the fungus Claviceps purpurea. The objects described here, although very much larger, of a different shape, and found in the soil, are also sclerotia, the resting stages of the toadstool A. arvalis.
A few months after bringing in the sclerotia, the man telephoned me to report pale fruiting bodies of
A. arvalis in his garden.