Plants and fungi share more in common than most people realize. Both are eukaryotes, meaning their cells contain a nucleus and other membrane-bound compartments. They’re both stationary organisms that anchor themselves to a substrate, reproduce using spores, and have cells reinforced by rigid walls. These overlapping traits are so striking that for over 200 years, scientists classified fungi as plants.
Why Fungi Were Once Considered Plants
When Carl Linnaeus built his classification system in the 1700s, he placed fungi squarely in the “Regnum Vegetabile,” the plant kingdom. The reasoning was straightforward: fungi don’t move, they grow rooted in place, and they lack the obvious features of animals. It wasn’t until 1969 that biologist Robert Whittaker formally proposed fungi as a “Third Kingdom,” distinct from both plants and animals. Genetic analysis has since confirmed that fungi are actually more closely related to animals than to plants on the tree of life. But the similarities between plants and fungi are real, even if they evolved independently.
Shared Cell Structure
At the cellular level, plants and fungi are built on the same basic eukaryotic blueprint. Both have a defined nucleus housing their DNA, mitochondria that generate energy, a Golgi apparatus that packages and ships proteins, and an extensive internal membrane system that creates specialized compartments for different chemical reactions. Most of these membrane-bound organelles are present across nearly all eukaryotic life, but plants and fungi share a few features that set them apart from animal cells specifically.
The most obvious is the cell wall. Animal cells are soft and flexible, held together only by a thin membrane. Plant and fungal cells both build rigid walls outside that membrane, giving them structural support. The key difference is composition: plant cell walls are made of cellulose, while fungal walls rely on chitin (the same material in insect exoskeletons). The function, though, is the same. Both walls maintain cell shape, resist internal pressure, and protect against environmental stress.
Both also contain large internal compartments called vacuoles. In plants, vacuoles store water and help maintain the turgor pressure that keeps stems upright. In fungi, vacuoles serve a similar storage and recycling role, breaking down waste and regulating internal chemistry. These vacuoles are connected to the cell’s broader transport network through tiny vesicles that shuttle materials between compartments. Animal cells have a rough equivalent in lysosomes, but the large, prominent vacuole is a feature plants and fungi share.
Neither One Moves
Plants and fungi are both sessile, meaning they stay put once established. This shared constraint has shaped how both groups solve the fundamental problem of finding resources without legs. Plants extend roots through soil and leaves toward sunlight. Fungi extend thread-like filaments called hyphae through whatever substrate they’re growing in, whether that’s soil, wood, or decaying matter. These hyphae branch and reconnect to form vast networks called mycelium, sometimes spanning enormous areas underground.
This stationary lifestyle also explains why both groups reproduce by releasing tiny, lightweight propagules into the environment. Since neither organism can seek out a mate or travel to a new habitat, they rely on wind, water, and animals to carry their reproductive cells to new locations. Being rooted in place has also pushed both plants and fungi to develop close partnerships with mobile organisms and with each other, a relationship that turns out to be one of the most important in terrestrial ecology.
Reproduction Through Spores
Both plants and fungi produce spores, single cells capable of developing into a new organism without fusing with another cell. Spores are small enough to be carried on air currents, sometimes traveling hundreds of miles before landing. They can also go dormant, surviving harsh conditions like drought or extreme cold until temperature, moisture, and other environmental cues trigger germination.
In fungi, spores serve a dual purpose: spreading the organism to new locations and waiting out unfavorable conditions. Some fungal species release millions of spores per day from a single fruiting body (the mushroom you see above ground). Plants use spores too, though the strategy is most visible in ferns, mosses, and other non-flowering species. Flowering plants have largely replaced spore dispersal with seeds, but the underlying reproductive cycle still includes a spore-producing stage. The reliance on lightweight, airborne reproductive cells is one of the clearest parallels between the two kingdoms.
How They Absorb Nutrients
Neither plants nor fungi eat the way animals do. Animals ingest food and digest it internally. Plants and fungi both absorb dissolved nutrients directly through their cell surfaces, a feeding strategy called osmotrophy. Water and minerals pass through cell walls and membranes via osmosis and active transport proteins that pull specific molecules inside.
The difference lies in what they absorb and where it comes from. Plants are autotrophs: they make their own sugars from sunlight and carbon dioxide, then absorb water and minerals from the soil through their roots. Fungi are heterotrophs: they can’t photosynthesize, so they feed on organic matter. To do this, fungi secrete digestive enzymes into their surroundings, breaking down complex molecules like cellulose and lignin into smaller pieces that can pass through the cell wall. It’s essentially digestion happening outside the body rather than inside it. But the final step, pulling dissolved nutrients across a membrane, works the same way in both organisms.
Mycorrhizae: Where the Two Kingdoms Meet
Perhaps the most remarkable connection between plants and fungi is that they literally fuse together underground. Around 90% of land plants form partnerships with mycorrhizal fungi, a symbiosis so ancient it likely helped plants colonize land in the first place. In these relationships, fungal hyphae weave into or around plant root cells, creating specialized contact zones called symbiotic interfaces where nutrients flow in both directions.
The exchange is straightforward. Fungal networks are far better at extracting minerals, especially phosphorus, from soil than plant roots alone. The fungi deliver these minerals to the plant. In return, the plant supplies the fungus with sugars produced through photosynthesis, which the fungus needs because it cannot make its own food. Both partners benefit: plants with mycorrhizal connections show improved mineral nutrition, better water absorption, faster growth, and stronger disease resistance. The fungi, meanwhile, depend on their plant hosts for the carbon that fuels their growth and reproduction.
These fungal networks don’t just connect one plant to one fungus. A single mycelial network can link entire plant communities, creating what researchers have called the “wood-wide web.” Through this network, nutrients can transfer horizontally between plants, with larger, established trees sometimes subsidizing smaller seedlings growing in the shade. The partnership highlights something fundamental about these two kingdoms: despite being separate branches of life, their biology is so compatible that they’ve spent hundreds of millions of years growing into each other.