Looks like cup fungi from the pezizaceae family. They probably live of the mulch and will do no harm to your tree. I see them often here, most often close to pines

Oh good! Thanks for the confirmation. My first thought was honey fungus!! until I saw it looked different. Then I figured it was my recent expansion in the use of mulch. :-)

This appears to be artillery fungus, sphaerobulus species. Once the cups fill with water, the fungal spores are expelled with surprising force. Light sensitivity plays a role and the spores attach themselves to light colored surfaces including cars, house siding, anything white. The spores are extremely hard to remove once they have attached themselves to a surface. They grow in/on bark mulch and do no harm to plants but they do spread rapidly and can create a real mess in the wrong place. The bottom 3 or 4 feet of a neighbor's white house became pretty well coated a few years ago. He's still battling it even though most of the bark mulch was replaced with gravel.

Probably one of the Peziza's (brown cup fungus) as huggorm suggested. I had a few in my mulch this spring as well, and they looked exactly like bill_minn's photos. Here's what one of them looks like today: