Large, whitish cap up to 20 cm across, usually yellowing on the surface.  There is a well-developed ring which splits into a cogwheel-like effect on the underside. It smells of aniseed. Spores are dark purple-brown and the flesh usually slowly stains yellow when cut or bruised.

There are several similar species - the toxic Yellow Stainer and some inedible related species quickly turn yellow when cut or bruised.

smell

Photograph from top down and from side, and underneath a young specimen before opened fully

Grassland - roadsides, pastures, fields and parks, on nutrient-rich soil.

Late summer through autumn.

A widespread and fairly common species in Britain.

Fairly common in Leicestershire and Rutland.

https://www.first-nature.com/fungi/agaricus-arvensis.php