Neither Plant nor Fungus: Decoding the 900+ Species of Myxomycetes

If you look at a slime mold in the wild, your first instinct is likely to classify it as a fungus. It grows on rotting wood, thrives in the damp, and produces “spores.” But in the world of biology, the name “slime mold” is a historic mistake.

Slime molds are not fungi, and they are certainly not plants. They belong to a massive, diverse group of eukaryotic organisms known as protists. They are the “outsiders” of the tree of life—a 600-million-year-old lineage that defies our standard categories.

The Case Against Fungi

For centuries, slime molds were studied by mycologists (fungi experts). However, the cellular reality is fundamentally different:

1. Chitin vs. Membranes: Fungi have cell walls made of chitin (the same stuff in shrimp shells). Slime molds lack these rigid walls during their active stage; they are bounded only by a flexible, pulsing plasma membrane.
2. Feeding vs. Absorption: Fungi eat by secreting enzymes onto their food and “absorbing” the soup. Slime molds are active hunters. They “cruise around” their environment, surrounding their prey (bacteria and microbes) and swallowing them whole in a process called phagocytosis.

The Case Against Plants

While some slime molds can look like delicate stems or corals, they share nothing with the plant kingdom:

• No Photosynthesis: Slime molds cannot turn sunlight into energy.
• Active Movement: Unlike plants, which grow toward the light in slow motion, slime molds can move up to 4 centimeters per hour, actively choosing their path based on chemical “scents.”

The 900+ Species: A Global Swarm

There isn’t just one “blob.” There are more than 900 recognized species of myxomycetes found on every single continent on Earth.

• The Survivors: They have been on our planet for at least 600 million years. To put that in perspective, they were already ancient by the time the first dinosaurs appeared.
• The Architects: From the bright yellow Physarum polycephalum to the iridescent Diachea leucopoda, each species has evolved a unique way to navigate the “decay” of our planet.

Why Classification Matters

Calling a slime mold a “mold” is like calling a dolphin a “fish.” It obscures the biological truth. By correctly identifying them as protists, we can begin to appreciate their true nature: they are giant, mobile, predatory single cells.

They represent a “Third Way” of life—one that combines the mobility of animals with the reproductive strategy of fungi and the structural simplicity of amoebae. They are a billion-year-old proof that you don’t need a brain, or a branch, or a mushroom cap to be a success on Earth.

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Want to see where the blob fits in the tree of life? Check out our Phylogeny Interactive Map.

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Origin and E-E-A-T

• Source: SciShow: “Slime Mold: A Brainless Blob that Seems Smart.”
• Scientific Name: Eumycetozoa (Slime Molds).
• Key Concept: Phagocytosis and Protist Classification.