No. Molds are fungi, and slime molds are not fungi at all. Is slime mold a fungus? No, and the slime mold vs fungus question gets settled at the cell wall. The yellow blob on your mulch looks like something a fungus would build. You watch the blob creep across bark, dry into a crust, then puff out a cloud of spores when you kick the pile. Every one of those habits is borrowed. The body underneath belongs to a separate kingdom.
The word mold is the part that does the damage. A mold is a fungus by definition, so the common name hands you a family tie that was never there. The slimy half of the name is honest enough. The other half sends you hunting for a fungal fix. There is no fungus in your yard to fix, and that one bad word has cost gardeners more money than anything else on the shelf.
Check the wall and the case closes. Fungi build cell walls out of chitin, the same tough material in a beetle shell. Slime molds carry no chitin at all. Their spore walls come out smooth and hold cellulose instead, a plant material that no fungus uses. So the part that looks most fungal to you, the dusty spore mass, turns out to be the exact part that gives the whole thing away under a microscope.
Feeding splits the two apart just as cleanly. A fungus sits in food, breaks that food down outside the body, then soaks the pieces up through the cell walls. A slime mold goes and gets the meal instead. The blob flows over bacteria, fungal spores and maybe smaller protozoa, then wraps around the lot and pulls the whole catch inside. That is engulfing, and an amoeba feeds the same way. A rigid fungal wall makes the move impossible, and you will not find a true mold anywhere that can pull the trick off.
The formal placement backs that up. The myxomycetes, the group behind most of the blobs on your mulch and lawn, sit inside a phylum called Amoebozoa. That group forms one branch on the tree, with a single shared ancestor, and it is more closely related to amoebas and certain seaweeds than to fungi. The wider name is messier than the science. UC Berkeley points out that the three main groups we all call slime molds do not form a clade at all. Looks alone got the three filed together.
So the right label is protist, the catch-all kingdom for living things that are not animal, plant or fungus. That word does real work at your garden center. A fungicide is built around fungal chemistry, and the spray goes after parts a slime mold never grew, so you have nothing for the product to act on. Empty the whole bottle over a yellow patch and you change nothing. Skip the purchase and put your money toward mulch you actually need.
Check the label for the target organism before you buy. Anything sold for mold or mildew aims at fungal structures, and a slime mold has not one of those parts.
The common name is a holdover, and slime mold is easier to say than a Latin class name. What you have sitting on your mulch is much closer to an amoeba than to anything fungal. The blob crawls, hunts bacteria, and shows a fungus-like face only in the spore stage at the end of the run. Knowing which kingdom you are dealing with saves you a purchase and a fair bit of worry about your plants.
Read the full article: Slime Mold: Not a Fungus, Not a Problem
