You mulch your garden for several reasons but one of the most popular reasons is because it makes your yard look nicer. So, it's a bit of a gut punch when you walk out into your newly mulched garden to find what some describe as a looking like vomit on their mulch. Don't worry, there haven't been any wild frat parties in your front yard while you slept and your dog is probably not sick. Instead this is a natural process.
What Is Growing in My Flower Bed?
What you are seeing is fungus? Sometimes you see it in the way of mushrooms but these piles of "pukey" material you find in your mulch serves the same purpose. They are helping to decompose natural material in your garden. In this case, it's your mulch. There is no one sort of mulch that is more susceptible to this problem.
Slime Mold
In this case you are looking at a slime mold. According to the University of Connecticut, slime molds feed on the bacteria that are feeding on the mulch, not actually eating the mulch directly.
While it causes no damage to your yard, most people choose to get rid of it. The easiest way to do this is to shovel it off, being careful not to break it up as the small spores will spread elsewhere and continue to plague your gorgeous garden.