Why were slime molds not considered fungi?

Slime molds: Old slime

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In the Maisinger Gorge west of Lake Starnberg, three men crawl through the undergrowth in the pouring rain. They wear headlamps, rain jackets, mountain boots and collars with magnifying glasses dangling from them. You are looking for a bizarre way of life. According to myxomycetes, in German: Schleimpilzen.

The mug shots shown by expedition leader Peter Karasch from the Munich Mushroom Association and his colleagues appear as if from another world. The slime molds, which are only a few millimeters in size, look like filigree lanterns, colorful billiard balls or red bottle brushes when magnified 50 times.

"Strictly speaking, we are not at all responsible for myxomycetes," says Karasch. Because actually slime molds are not mushrooms at all. Neither are they plants or animals. Their development cycle is unique in the world of living things. If the wind carries a myxomycete spore into a damp corner of the forest, it becomes a unicellular amoeba. This myxamoeba feeds on bacteria. Your goal is to unite with another myxamoeba - the simplest form of sex there is. Meanwhile, the nuclei of the two fuse, creating a so-called plasmodium. Its cell nuclei continue to divide every eight hours without the cell dividing itself. It gets bigger, discolored, and produces mucus.

"Plasmodia are very seldom found because they are hiding in the leaves or rotten wood," says Andreas Kuhnt, who is looking for slime mold, while turning a rotten tree trunk. He means it literally: Plasmodia can run and cover several meters. In the centimeter-sized giant cells, some of which have millions of cell nuclei, vein-shaped structures are created that function like human muscles. They contract every minute, relax again and in this way pump cytoplasm back and forth. If a Plasmodium sniffs something edible with its chemical receptors, such as a bacterial colony or an edible mushroom, the flow in this direction takes a little longer than in another. The slime moves forward a little - at a speed of around one centimeter per hour.

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But so far the Bavarian slime mold hunters have not detected any plasmodia. Actually, they had hoped for the sunshine promised by the weather report. In warm periods after long rainy seasons, the otherwise light-shy plasmodia climb grass and tree trunks, some species even climb up into the treetops. There their mucus hardens into stalks and fruit capsules, and the cell nuclei turn into spores. "If you are not careful, it also happens at home on your desk," says Kuhnt and tells of a find that stole out of its cardboard box at an unobserved moment, climbed onto the next best identification book overnight and formed fruit bodies there.