Leucoagaricus leucothites was formerly called Leucoagaricus naucinus and with the state of flux in taxonomy at present, it might have another name next year. It is a mushroom of worldwide distribution, widely known as an edible species but often recommended as a species to be avoided because it shares so many features with a couple of deadly Amanitas. For this reason nobody should attempt to eat these unless they are completely confident in being able to distinguish an Amanita.
I spotted the specimens above by the side of the road, which is a common place to find them. The caps are bright white with a satin texture. The shape of the large specimen in the picture is characteristic of this species. The underside features a hollow stem that widens a little at the base, but does not have a sac or volva like Amanita or Volvopluteus. The gills are at first white but darken a little at maturity. The spore print is bright white.
It is always a little scary eating something new but even more so when it is something with white gills and a white spore print. Nevertheless, after much checking and re-checking I fried some up and did a taste test. From descriptions elsewhere I had expected something more; it tasted just like Volvopluteus gloiocephalus. The mature specimen even looks a little like Volvopluteus.
One can only wonder how species like this manage to spread so far and wide. Apparently the spores of this one germinate very readily in a wide range of media so perhaps that has something to do with it. Anyway, another of our introduced species that is edible for what it is worth.