The genus Lacrymaria contains species with dark brown gills that are very similar in colour to Agaricus. Today I spotted the mushrooms below on the side of the road in the middle of Karri forest near Pemberton in SW WA.
The gills were a dark chocolate brown.
From the above shot a couple of things stand out. Firstly, the gills are attached to the stipe. This differs from Agaricus where the gills are always free. Secondly, the stipe has split into a number of strips. This does not happen with Agaricus.
A close-up of the gills also shows that they are blotchy in appearance, which we do not seen in Agaricus.
Under UV light the entire mushroom glows a lovely purple colour. Unfortunately I was unable to capture this colour on my iPhone.
Note: I have named this specimen from online images. It may be a native species that is not described.
Lacrymaria are not considered to be edible mainly because of taste rather than toxicity. It has a very thin flesh in any case so would not make much or a meal.