Yet another yard fungus. (Previously.) Most of what we get here are pretty normal, little beige mushrooms, but something about the unusually cool, wet summer must be encouraging the weirder ones. Or maybe something about the unusually cool, wet summer means that I spend more time outdoors, and am therefore in a better position to observe weird fungi. Whichever.
I'm not sure what species or genus this particular specimen is; according to Wikipedia, the color of the peridioles is a good indicator of the genus, and these being black means that this is probably a Cyathus.
Bird's-nest fungi are so named because they look like tiny little nests with eggs in them. They're not actually eggs, obviously -- instead, they're peridioles, which contain the spores for the next generation of fungi. The spores are dispersed by rain: the shape of the "nest" is such that a raindrop hitting it will eject the peridioles as far as possible (up to 3-4 feet / 0.9-1.2 m).
The houseplant/gardening consequence of bird's-nest fungi is basically zero: they don't attack living plants, and they're so tiny it probably wouldn't matter if they did. They make a living from breaking down the cellulose and lignin in dead wood into sugars, so you'll occasionally run into them in potting soil (which often contain composted wood). I can't find the post now (maybe I didn't actually write one?), but I've seen a clump of them growing out of the drainage hole of a plant at work once:
So not a big deal. Kinda neat, though.