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That is in the genus Coprinellus. They don't last long, and will deliquesce within a day or two.

It could be stinkhorns and they pose no threat. No control is needed.

https://extension.umn.edu/lawn-care/common-fungi

They are coprinoid mushrooms, but at this point very hard to tell exactly which. The caps turn into a mushy, spore-laden mixture and just so happen to stick to whatever they are touching at the time.

They are not considered harmful, by any means. You should not eat them, however, because some of the coprinoid mushrooms will cause serious discomfort.

Here is an article that will help you with the care of your plant:

https://www.gardeningknowhow.com/ornamental/bulbs/dahlia/grow-dahlias-in-containers.htm

Unfortunately, without photos I can't say much about the situation. Fungi are tricky, and you can worsen an issue by trying to treat it, but it can be an even bigger issue if it happens to be a detrimental fungus.

Generally, though, plants and fungi thrive in totally different conditions. If it is ideal for one, it is not ideal for the other. In most cases, the mushrooms that survive in less than ideal conditions are not detrimental to plants or trees.

Ir order to rid the area of mushrooms, you must remove the conditions in which they thrive. Most of the times, this will simply mean that the soil remains way too wet. Watering once the soil (NOT THE MULCH) dries down to about 3 or 4 inches, thoroughly. Though, in your area, there is rarely enough of a drought to water at all with mulch.

Treating with a fungicide may or may not help. Mushrooms generally won't respond to them quickly. This will need to be done over a whole season, along with keeping the area dry.

Here are some articles that will help you:

https://www.gardeningknowhow.com/ornamental/fungus-lichen

Unfortunately, your photos did not come through. I am unable to see the mushroom in question. There are a few species in the genus Hydnum, so it is important to be sure that this is what you have. As far as who to report to, Mushroom Observer is a good website to post findings. This is a place to note what and where you find something. You might be surprised to find others in your area that have documented the species, as well!

There are several medicinal compounds within the fungus. Please do not consume it until you have done enough research to be comfortable doing so. Even then, I would seek dosage advice from published medical studied. PubMed may have some information on this subject.

https://www.gardeningknowhow.com/ornamental/fungus-lichen/is-bleeding-tooth-fungus-safe.htm

You could move some to your garden, yes. It wouldn't do well in a properly kept compost pile.