Cap smooth or with dark fibrillose scales, usually dull in colour (some of the indigenous pecies with dark brown scales);, stalk central with a well-developed ring;, gills always pink when immature, becoming dark chocolate brown as spores develop, more or less free. Stalk typically breaks cleanly away from the cap. Spore print chocolate brown. Saprobic on the soil.
Seven indigenous species have been reported, although the genus has been rather poorly collected and a number of these species have been seen only rarely. There may be around 12 introduced species. The identity of Agaricus to the species level is often problematic without a good understanding of the kind of variation in appearance that can occur with changes in weather, age, or micro-site.
The indigenous species are typically found in forests, the exotic species in grassy areas, on lawns, in parks and in farmland. Included amongst the exotic species is the "field mushroom" and the "button mushroom", commercial strains of which are grown for sale in the shops.
Not all Agaricus species are edible. Those in which the flesh stains yellow at the base of the stalk often cause stomach upsets, sometimes severe. Agaricus xanthoderma is a name that has been used uncritically in New Zealand for a set of species all with this yellow-staining feature, probably all introduced. One of these species is common on lawns in northern New Zealand towns and cities, smaller in stature than most Agaricus species and with the very top of the cap having a small flattened area.
Care also needs to be taken not to confuse Agaricus with the deadly poisonous Amanita, mushrooms of similar stature and often with a ring on the stalk, but always with white spores and gills. Other white-spored mushrooms that can be otherwise somewhat similar in appearance and habitat to Agaricus include Chlorophyllum and Leucoagaricus.


NZFungi Entry

Agaricus arvensis

The Horse mushroom. Large mushrooms, cap up to 20 cm or more, an introduced species, always on grass in parks, etc. The whitish cap sometimes stains slightly yellowish with age, but the flesh inside the stalk never stains yellow. Edible and good.

Agaricus campestris

The field mushroom. An introduced fungus, often seen in large numbers in heavily fertilised grassy areas in cities, as well as on farms. Edible and good. Agaricus cupreobrunneus is found in similar places, but has a brown, slightly hairy cap.

Agaricus lanatoniger

One of the indigenous species. Has been collected in several different kinds of forest from Nelson northwards.