But Caroline Aitken, a fungi expert, gave it a quick clean and placed it in her basket alongside the rest of the day's pick from the New Forest, declaring: "It's simply too good to waste."
This weekend in Britain is the peak autumn season for fungi picking, and food lovers believe the nation should wake up to the rich harvest waiting in forests across the country. While the French, Italians and the Eastern Europeans are out picking the free ceps, chanterelles in our parks and countryside, the British are in the supermarket buying less tasty, cultivated ones.
A lack of knowledge of the line between edible and poisonous is what keeps most Britons from enjoying fungi, unlike most of Europe, where a shared knowledge, passed through the generations, enables whole families to go mushroom picking.
Michael Jordan, chairman of the Association of British Fungus Groups, said this would be one of the peak weekends for studying fungi in Britain, He said the country was "very much behind" most of Europe in understanding both edible and poisonous fungi, although interest was growing and more than 600 people would out this weekend with the Association.
Alex and Caroline Aitken are knowledgeable exceptions, the position of their Michelin-starred restaurant in the New Forest enabling them to pick and enjoy wild fungi. Mrs Aitken, who will make these forays regularly during autumn, ignores many varieties of smaller edible fungi, which she knows that Alex, her husband, wild food enthusiast and chef at the couples' Michelin-starred restaurant, Le Poussin at Whitley Ridge, in the heart of the Forest, will not want to cook.
"Why bother with the lesser ones that don't taste that great when you have all these magnificent tasting prime fungi like the ceps and other boletus varieties?'' she said on a three-hour walk. She then finds several more large brown fungi, with solid stems and caps that vary between golf and tennis ball in size. These are more smaller ceps - also known as 'Penny Buns' - and several other boletus varieties.
She also picks some small, white, Devil's Purse puffballs - "they taste like sweetbreads" - some saffron milk caps, a huge parasol mushroom, a few russulas and a fragment of Sparrassis crispa, the so-called "cauliflower mushroom", just some of the 50 or so edible varieties, out of around 3,000 larger species of fungi. She searched in vain for the prized wood chanterelles - "too early, not enough rain" was Mrs Aitken's verdict.
Twenty-five years' experience enables her to avoid not only the tasteless and less interesting ones, like the orange milk cap that exudes milk, and the primrose russulas that taste just too peppery, but also the known poisonous varieties, such as the startling red and white fly agaric or the poison pie.
But these do excite Peter Marren, a naturalist, writer and fungus expert also on the walk, who seizes on a small inoffensive looking mushroom, which he declares to be a false death cap. "False, because obviously unlike the death cap itself, which it resembles, it won't kill you and, actually, this one is harmless, but not terribly good for you. You can survive a death cap, which is the most deadly of all, but you will probably need new kidneys.''
He clearly gets a frisson of excitement from the more exotic varieties. It doesn't stop him nibbling away and offering samples around for tasting. "There's always that risk with fungi, isn't there?" Mr Marren also said that it was important that people should learn how to identify and cook edible fungi.
Back at the restaurant, Mr Aitken is delighted with the pick and prepares a spectacular meal designed to illustrate the diverse possibilities of fungal cuisine. Nothing is wasted - scraps go into stocks or to make mushroom ketchup; any abundance of ceps will be dried and preserved.
Firstly, there are a selection of seven different mushrooms, each tasting distinctly differently, each cooked very lightly, served around a chicken and mushroom "sausage". Then, a single scallop is served topped with the exotic, black horn of plenty mushrooms and a puree of ceps. Finally, some rare venison, with more ceps.
"I love cooking with wild fungi because of the seasonality, and the variety of tastes and textures. It's a real flavour of the forest on your plate.'' Not everyone, he accepts, will want to turn fungi into haute cuisine. "There are always more simple soups, ragouts and risottos to be made as well.''
Visit the Association of British Fungus Groups at www.abfg.org
Alex Aitken's top edible fungi
J MORELS: A spring fungus, not usually found in woodland. Great for drying or stuffing the bigger ones
D CEPS/PENNY BUNS: Sweet and nutty when fresh, smoky and musty when dry. Great with rich meats like venison or beef
J GIROLLES/YELLOW CHANTERELLES: 'Delicious when very lightly cooked,' said Alex. Go well with fish
D CAULIFLOWER FUNGI: A lovely, lightly flavoured yellow fungi, with a distinctive pine and smoky taste
J HORN OF PLENTY/ TROMPETTE DE MORT: Exotic looking, small black fungi, with a distinctive nutty flavour
D DEVIL'S PURSE PUFFBALL: Only small ones can be picked; big ones fill with slime. A vegetarian 'sweetbread'