Jack Murrell, of Manapouri, asks :-
From my memory this mushroom is the first time seen at Manapouri. Is it deadly?
Jerry Cooper, a fungal scientist at Landcare Research, responded.
The veil over the gills in the photo is a 'partial veil' and not a universal veil as is found in the deadly species of Amanita. The universal veil envelopes the cap and breaks up on maturity leaving fragments on the surface (the characteristic white spots on the cap of the red Fly Agaric) and it also leaves a cup at the stem base (the volva). Neither feature of a universal veil is present in this fungus and it is not an Amanita. The deadly Amanita phalloides (a greenish yellow colour) is known in northern parts of New Zealand growing with oaks, with which it has a mycorrhizal association. The Destroying Angel (Amanita virosa) does not occur in New Zealand.
The mushroom in the photo is immature because the partial veil has not yet broken to reveal the maturing gills, and it is the colour of those mature gills (and the spores) that would allow identification of the mushroom. The presence of a partial veil, colour, and the cog-like pattern on the partial veil suggests this is most probably Agaricus arvensis, the Horse Mushroom, and it would have pink gills turning brown, a brown spore print, and is edible. It is an introduced mushroom of open fields. See naturewatch.org.nz/observations/2843777