Wildlife Spotting

Not all Amanitas have volvas present, some of them have an abruptly bulbous base like this. The more I look at that broken cap though, I agree it doesn't look like an Amanita.

If it really was a volva I'd agree with you on Amanita, however as Mark now agrees it's just the stem base I think Amanita is unlikely due to the cap texture. Probably a young Agaricus who's spores haven't developed yet leaving its gills still pale. Could be something else.

It is an Amanita species.

What exactly do you mean by a solid volva? I only ask because I suspect you might be referring to an abruptly bulbous stem base protruding from the ground rather than a volva. The picture doesn't show the base of the stem particularly clearly so I could well be missing it but I can't see a volva. To be clear (not saying you don't know this already), a volva is sac-like tissue around the base of the stem which is left over from when a universal veil was wrapped around the whole mushroom so it's likely to be somewhat cup shaped. Also to me this looks to me like a young Agaricus species which wouldn't have a volva but I'm not confident on that ID. P.S. Since the mushroom's gills are still protected by a partial veil we can be confident that it is not mature. Therefore you are unlikely to be helping to spread the spores of the fungus as they won't be developed yet and would produce millions more once it does mature. That being said, I don't think it is particularly destructive to cut open a few immature mushrooms here and there as it is only a temporary reproductive organ of a fungus who'll go on to produce many more fruiting bodies (mushrooms) in it's lifetime. It won't affect the perennial organism beneath the ground, just this particular shot at reproduction.

Why did you break open the poor plant?