Calvatia gigantea (giant puffball)

Calvatia gigantea is widespread and found in temperate regions throughout much of both the northern and southern hemispheres. The species occurs throughout the British Isles.

Example of size of the giant puffball (Image: Geoffrey Kibby)

This distinctive species can be recognised by the large, rounded fruitbody, 20 to 60 cm across, with no stipe (stalk). The surface is white at first, later somewhat discoloured to yellowish or pale olive-brown. The surface is matt, finely velvety and somewhat like kid leather to the touch. It later becomes smooth, rather papery and breaks away to reveal the gleba (fertile tissue) which contains the spores. The gleba is white at first, then yellow to dark olive-brown. The spores are olive-brown in mass, rounded, 4 to 5 μm wide, with a finely warted surface and are produced in abundance.
 

Although most mature specimens are football-sized, some grow much larger. The largest British specimen ever measured was 162 cm (64 in) in circumference, and claims for American specimens around 1.5 m across have been made! Such large specimens may be over 20 kg in weight, though about 4 kg is more usual.

Giant puffball in the 'rough' of Seahouses golf course, Northumberland (Image: seahouseswebsite.co.uk)

Calvatia gigantea is one of over 20 British species broadly referred to as ‘puffballs’. As the name suggests, these all produce a powdery spore mass at maturity, developed in the fertile tissue (the gleba) inside a rounded or club-shaped fruitbody. True puffballs belong to the genus Lycoperdon, of which a dozen or so species occur in Britain. These all have a well-defined circular pore at the top, through which the spores are released by a bellows mechanism, usually due to falling rain drops. Other puffballs have a wall which breaks open irregularly to expose the spore mass. They include the large ‘mosaic puffball’ (Handkea utriformis) found in unimproved grasslands, and the ‘pestle-shaped puffball’ (Handkea excipuliformis) which usually occurs in woodland. These differ from giant puffball particularly in having a well-defined sterile base.

This species is perhaps the most prolific of all fungi, and perhaps of all organisms. The total number of spores produced by a single, average-sized fruitbody is estimated at around 7 trillion - with large specimens producing many more. We are not over-run with puffballs, however, as spore viability is low, and most do not germinate. In fact experiments have reported a spore germination rate of less than 0.001%.

No specific threats have been identified, and the giant puffball is not currently considered as of conservation concern in the UK. It has not been evaluated by IUCN, but is protected in parts of Poland, considered of conservation concern in Norway, and rare in Lithuania.

This is an excellent edible fungus, long sought after for its culinary value. It was well known to the Greeks and Romans, and attempts to cultivate the species, though unsuccessful, were made in Denmark more than 150 years ago. It has also been used in medicine, for example as a styptic (to contract tissues and reduce bleeding) and for wound dressing. The anti-cancer agent calvacin has been isolated from young fruitbodies and especially cultures of giant puffball, as well as from some other puffball species. It has proved effective against tumours, but unfortunately is present only in tiny quantities. As might be expected for such a well-known fungus, giant puffball has had a variety of folk uses in Britain and elsewhere. Use as tinder was frequent, and it has also been used in beekeeping. Fumes from smouldering fruitbodies placed beneath the hive calm the bees and allow easier access to the hive.

Calvatia gigantea has occasionally been recorded in the Gardens but is not common.

Preserved specimens of Calvatia gigantea from throughout its range are maintained in the Kew Mycology Herbarium and, although not accessible to the general public, are available for study by research workers worldwide.