Fungi are plants.

Putting fungi among plants once made practical sense. Mushrooms and molds grow from soil or other surfaces, usually stay fixed in one place, and often produce branching structures. In older classifications built largely from visible form and lifestyle, they fit comfortably within botany.

Closer study revealed a very different way of living.

Plants use photosynthesis to capture light energy and make organic material. Fungi do not. Instead, they release digestive enzymes into the material around them and then absorb the smaller molecules produced by that digestion.

Their cells also differ in important ways. Fungal cell walls contain large amounts of chitin, whereas plant cell walls are built mainly from cellulose. Their reproduction and cellular organization follow their own patterns as well.

By the twentieth century, treating fungi as unusual plants had become increasingly difficult. Robert Whittaker’s five-kingdom system in 1969 gave them a separate kingdom.

DNA and RNA comparisons later made the evolutionary separation even clearer. Fungi belong to a branch more closely related to animals than to plants.

Modern fungal classification continues to change as genetic relationships are refined, but fungi themselves are firmly established as a distinct major lineage.