I found a little guy growing in my window planter. I'm guessing he probably falls into the category of "little brown mushroom", and is best left uneaten, but if this description sounds familiar to anyone, I'd love to hear more. Must've popped up really quickly. The cap is 3/4", sort of ovoid, beige darkening to brown at the top. The gills are white. The stalk broadens toward the base, and does not feature any ring. I'm not quite sure how to take a spore print on a cap this vertical.