When I left my PhD student office at the Museum of National Antiquities I rescued a couple of angel wing begonias. One has recently been joined in its pot by spontaneously appearing yellow fungus. Today four sizeable mushrooms popped up! And Dear Reader William identified them: they’re Yellow Houseplant Mushrooms, Leucocoprinus birnbaumii. That’s an eminently sensible name for a mushroom, by the way.