Deathcap (Amanita phalloides) is one of the most poisonous mushrooms in the British Isles and it can certainly be found growing in the New Forest.
In fact, in the south of England it may be frequent and widespread. It is probably the most notorious and aptly named of all mushrooms.
The New Forest has large areas of woodland with oak and beech trees, with which the mushroom has a special relationship. The Deathcap is not uncommon – especially so, on the less acid and more alkaline sites, such as in the south of the New Forest. It may be seen growing singly or in small groups, but it can even occasionally form fairy rings too. The fruiting bodies will appear from mid-summer to the end of autumn.
The cap is totally smooth and convex when young, then expanding to 10-12 cm across. The gills are crowded and white. The cylindrical stem is up to 15 cm long and is mainly white as well, but may be flushed with the olive green colour of the cap. The white fragile pendulous ring quickly falls away to leave the stem bare. The base of the stem is always surrounded by a persistent white volva (or egg cup like bag), in common with all fungi of this genus. The fruit body has a sweet fruity odour possibly akin to rose petals. However as the mushroom matures the smell becomes stronger and becomes unpleasant to some.
There is also an all-white form of Deathcap (Amanita phalloides var.alba) which although less common, can unfortunately, seriously confuse identification.
The Deathcap is responsible for more deaths from fungal poisoning that any other mushroom. It contains a number of toxins which are not reduced by freezing or cooking. Only a small section of the cap is needed for a fatal dose. Apparently, a few hours after ingestion of the mushroom it can cause nausea, vomiting and diarrhoea, then after a few days a feeling of recovery and wellbeing. However, after a week to 10 days, there is death from kidney and liver failure.