Fungi and plants share a handful of fundamental traits, including cell walls, a eukaryotic cell plan with membrane-bound nuclei, and an anchored lifestyle spent rooted in one spot, but they differ in almost every aspect of how they feed, build their bodies, and reproduce. Plants capture sunlight and convert it into chemical energy; fungi absorb nutrients from their surroundings, breaking down dead or living organic matter to survive. Their cell walls are made of entirely different materials, their genomes are organized differently, and their ecological roles barely overlap. For centuries these organisms were lumped together, and untangling why reveals a lot about both of them.
Why Fungi Were Once Classified as Plants
In the early days of biological classification, fungi sat squarely inside the plant kingdom. They do not move. They grow from a fixed position. Many of them sprout upward from soil. To naturalists working before microscopes and molecular tools existed, that was enough. Algae and bacteria were lumped in with plants too. It was not until the mid-twentieth century that a five-kingdom model separated fungi into their own kingdom, acknowledging the deep biological gulf between the two groups despite their surface resemblance.
The superficial similarities are real, though. Both fungi and plants are eukaryotes, meaning their cells contain a nucleus enclosed by a membrane along with other membrane-bound compartments. Both are surrounded by a rigid cell wall, which animal cells lack entirely. Both tend to be sessile, growing in place rather than moving to find food. And both reproduce using spores or seeds that can disperse widely and remain dormant until conditions improve. These shared features are why the confusion persisted for so long.
Cell Walls Built From Different Materials
The cell wall is probably the single most instructive place to see how fungi and plants converge on the same structural strategy while using completely different chemistry. Plant cell walls are built primarily from cellulose, a long-chain sugar polymer that gives wood its strength and cotton its fiber. Fungal cell walls are built instead from chitin, glucans, mannans, and glycoproteins.1PubMed. The structure and synthesis of the fungal cell wall Chitin is the same tough material found in insect exoskeletons and crab shells, which gives you a sense of how different the fungal approach is from what plants do.
A review comparing fungal and plant cell walls during digestion spelled out the contrast plainly: the plant cell wall is largely composed of cellulose fiber, while the fungal cell wall relies on beta-glucans and chitin.2ScienceDirect. Comparison of the behavior of fungal and plant cell wall during gastrointestinal digestion and resulting health effects: A review Both walls serve the same basic purpose: they define the cell’s shape, protect the membrane-bound interior, and provide structural rigidity. But the raw ingredients are chemically unrelated, a sign that the two groups evolved their walls independently rather than inheriting the same blueprint from a shared ancestor.
Even the sterols embedded in their cell membranes differ. Plants use phytosterols, fungi use ergosterol, and animals use cholesterol. Despite these chemical differences, all three types of sterols perform the same job: keeping the cell membrane in a flexible-but-stable state that allows essential biological processes to work.3PubMed Central. Sterols and membrane dynamics This is a recurring theme when comparing fungi and plants. The functional problem is the same; the molecular solution is different.
Feeding Strategies Could Not Be More Different
The biggest biological divide between fungi and plants is how they get energy. Plants are autotrophs. They run on photosynthesis, using chlorophyll to capture light energy and convert carbon dioxide and water into sugars. This is the defining feature of plant life and the reason plants are green.
Fungi have no chlorophyll and cannot photosynthesize. They are heterotrophs, meaning they must obtain carbon and energy from organic matter produced by other organisms. Most fungi do this by secreting enzymes into their environment that break down complex molecules externally, then absorbing the resulting smaller molecules through their cell walls. This absorptive feeding style sets fungi apart from both plants, which make their own food, and animals, which ingest food and digest it internally. It is worth emphasizing that this is not a minor metabolic detail; it shapes everything about how fungi grow, where they live, and what role they play in ecosystems.
Growth Patterns and Body Plans
Plants and fungi grow in visually similar ways, both extending from tips and branching outward, but the underlying body plans are quite different. The main body of most fungi is a network of microscopic filaments called hyphae, which collectively form a mass known as mycelium. This mycelium often lives hidden inside soil, wood, or another substrate. What you see when a mushroom pops up is actually just the reproductive structure, the equivalent of a flower on a plant, while the real organism sprawls unseen below.
Fungal hyphae grow by tip extension, with a large volume of internal material contributing to the rapid assembly of new wall at the growing point. A vesicle-based delivery system shuttles building materials to the tip, allowing hyphae to extend at high rates.4Philosophical Transactions of the Royal Society of London. B, Biological Sciences. Growth and form in lower plants and the occurrence of meristems Plants also grow from tips and specialized growth zones, but their body plan is far more complex. A typical plant has differentiated roots, stems, leaves, and vascular tissue that transports water and sugars over long distances. Fungi lack true roots, leaves, or vascular systems, though their hyphal networks can shuttle nutrients across surprisingly large distances in their own way.
An interesting parallel exists in internal transport. In plant phloem, pressure-driven flow moves sugars through perforated sieve plates connecting individual cells. In certain fungal hyphae, cytoplasmic streaming moves material through pores in the septa, the cross-walls that divide hyphal segments. Researchers have noted the functional comparison between these two systems.5Developmental Cell. Streaming-Formed Subcompartments Depend on the HDA-2 Epigenetic Regulator and Provide Nuclear Differentiation in Fungal Hyphae Once again, the theme is convergence: different organisms arriving at functionally similar solutions through different evolutionary paths.
Both Respond to Gravity, but Not Identically
One of the more surprising similarities between fungi and plants is gravitropism, the ability to sense and grow in response to gravity. Mushroom stems orient themselves vertically, and the apex of the stem makes the most immediate gravitropic adjustment, reallocating growth resources to curve upward.6PubMed. Perception and response to gravity in higher fungi–a critical appraisal Plants, of course, are famous for this: roots grow downward and shoots grow upward in response to gravity.
Researchers who compared the two responses in detail found striking parallels. In both plants and fungi, the bending mechanism is the same: one side of the growing organ elongates faster than the other, creating a curve. The distribution of growth is similar too, with the most active growth occurring just behind the tip. Both also show a substantial time delay between sensing gravity and responding, suggesting complex internal signaling is involved.7Plant, Cell & Environment. Comparison of plant and fungal gravitropic responses using imitational modelling
The differences were telling, though. Fungal stems almost always returned precisely to vertical, while some plant organs settle at stable angles away from vertical. Fungal gravitropism rarely overshot or oscillated past the target orientation, whereas many plant organs overshoot and wobble before settling. And the overall physiological rules governing the gravitropic response of the bread mold relative Phycomyces followed the same “sine law” that describes plant gravitropism, yet diverged in other mathematical patterns.8PubMed. The sporangiophore of Phycomyces blakesleeanus: a tool to investigate fungal gravireception and graviresponses The basic toolkit looks shared; the fine-tuning is specific to each kingdom.
Reproduction and Life Cycles
Both fungi and plants alternate between sexual and asexual reproduction, and both use spores as dispersal units at various life stages. Beyond that broad similarity, the details diverge sharply. Plants typically alternate between a haploid generation (with one set of chromosomes) and a diploid generation (with two sets), and in most familiar plants the large visible organism is the diploid phase. Fungi are far more variable. Many common fungi, including bread molds and most mushroom-forming species, spend most of their lives in a haploid state or in an unusual condition where two genetically different haploid nuclei coexist in the same cell without fusing.
Recent work tracing the early evolution of fungi found that the oldest fungal lineages, the zoosporic fungi, were frequently characterized by diploid-dominant life cycles, and that at least one major group shows an alternation of haploid and diploid generations comparable to what plants do.9PubMed Central. Diploid-dominant life cycles characterize the early evolution of Fungi This suggests that the familiar haploid-dominant pattern of most land fungi is actually a derived feature, not the ancestral condition. Plant life cycles, by contrast, trended in the opposite direction over evolutionary time: the diploid phase became increasingly dominant as plants moved onto land.
Shared Ancestry and Ancient Genetic Overlap
Fungi and plants are not closely related on the tree of life. In fact, molecular studies consistently place fungi closer to animals than to plants. Yet the two groups share a surprising amount of ancient genetic material. Extensive analyses of gene families found that among roughly 2,600 groups of related genes shared across animals, fungi, and plants, at least 300 still retain evidence of gene duplications that happened before these three kingdoms split apart.10PubMed Central. Phylogenetic detection of numerous gene duplications shared by animals, fungi and plants Those shared duplications point to a deep common heritage, even though the two lineages have been evolving independently for well over a billion years.
Fungal genomes themselves are strikingly compact compared to plant genomes. A survey of 172 fungal species found genome sizes ranging from about 9 million to 178 million base pairs, with most falling in the range of 37 to 46 million base pairs depending on the major group.11PubMed Central. The diversity of fungal genome Plant genomes are routinely many times larger. The model plant Arabidopsis has a genome of about 135 million base pairs, and many crop plants measure in the billions. Genome size does not map neatly onto organism complexity, but the difference reflects the very different evolutionary pressures acting on each kingdom.
The Symbiotic Relationship Between Fungi and Plants
Perhaps the most fascinating intersection of these two kingdoms is mycorrhizal symbiosis, the ancient partnership between plant roots and soil fungi. Roughly 80 to 90 percent of land plant species form some kind of mycorrhizal association. In the most common type, arbuscular mycorrhizal fungi penetrate root cells and set up elaborate exchange structures. The fungus delivers mineral nutrients, especially phosphorus, to the plant. In return, the plant supplies the fungus with carbon, and recent work has shown that lipids are transferred from plant to fungus as a major carbon source.12PubMed. Nutrient Exchange and Regulation in Arbuscular Mycorrhizal Symbiosis
The nutrient exchange is finely regulated. Phosphate transporters in the fungus can switch between importing and exporting phosphorus depending on local concentration, ensuring that neither partner wastes resources.13Trends in Plant Science. Nutrient sensing and transport in mutualistic root-fungus associations This is not a crude trade but a sophisticated molecular negotiation, and when the balance shifts, the relationship can slide from mutualism toward parasitism in either direction.
Beyond mycorrhizae, fungi form other remarkable partnerships with photosynthetic organisms. Lichens are composite organisms in which a fungus builds an entirely new body structure together with algae or cyanobacteria, creating something neither partner can form alone.14PubMed Central. How to build a lichen: from metabolite release to symbiotic interplay Some lichens go further, incorporating both a cyanobacterium and a green alga as co-primary photosynthetic partners, demonstrating surprising flexibility in how the fungal partner selects its photosynthetic collaborator.15PubMed Central. Cyanolichens can have both cyanobacteria and green algae in a common layer as major contributors to photosynthesis
Fungal endophytes represent yet another dimension of the relationship. These fungi live entirely inside plant tissues without causing visible harm, and they have been found associated with every plant species studied in natural ecosystems. In mutualistic associations, endophytes can enhance plant growth, increase reproductive success, and confer tolerance to environmental stresses like drought or salinity.16PubMed Central. Unraveling the role of fungal symbionts in plant abiotic stress tolerance
When the Relationship Turns Hostile
For all their cooperative partnerships, fungi are also among the most destructive plant pathogens on Earth. Fungal diseases cause enormous crop losses worldwide, and pathogenic fungi use a range of strategies to invade and exploit plant tissue. Some fungi are necrotrophs, killing plant cells and feeding on the dead tissue. Others are biotrophs, colonizing living plant cells while keeping them alive, quietly redirecting the plant’s metabolism to serve the fungus. Specialized infection structures allow fungi to penetrate plant defenses, and once inside, they deploy virulence factors tailored to their strategy: necrotrophs secrete toxins, while biotrophs use molecular tools called effectors to suppress the plant’s immune responses and cell death programs.17PubMed Central. Plant Pathogenic Fungi
Plants, of course, fight back. They produce secondary metabolites with antifungal properties, and they have immune-like signaling pathways that detect and respond to fungal invasion. The biochemical arms race between the two kingdoms is intense. Some fungal pathogens have evolved the ability to mimic plant hormones like auxins and gibberellins, effectively hijacking the plant’s own growth and defense signaling to benefit the fungus.18PubMed Central. Secondary metabolites in fungus-plant interactions Pathogenic fungi also manipulate plant hormone pathways such as jasmonic acid and salicylic acid signaling to suppress immunity and promote their own survival.19PubMed Central. Effectors of plants pathogenic fungi and fungal like microbes: a comprehensive review on mechanisms, roles, and host interactions
Ecological Roles That Complement Each Other
In ecosystems, fungi and plants occupy fundamentally different niches that happen to depend on each other. Plants are primary producers, converting solar energy into organic matter that enters the food web. Fungi, particularly the saprotrophic species that decompose dead material, are primary recyclers. They are the main agents of plant litter decomposition, and their hyphal networks act as dynamic channels through which nutrients flow back into the soil. Their enzyme activity directly affects how fast nutrients are released from dead plant material and how much carbon dioxide returns to the atmosphere.20PubMed Central. Functional and ecological consequences of saprotrophic fungus-grazer interactions
Without saprotrophic fungi, dead plant material would accumulate and nutrients would stay locked in undecomposed organic matter. Without plants, fungi would lack their primary source of organic carbon. The two kingdoms form two halves of the terrestrial carbon cycle, one building organic molecules and the other tearing them apart. This complementary relationship is one reason terrestrial ecosystems function the way they do.
How Climate Change Is Reshaping the Partnership
As temperatures rise and atmospheric carbon dioxide increases, the ancient relationship between fungi and plants is being tested in new ways. A broad review of the literature found that elevated carbon dioxide, warming, and changes in rainfall all affect mycorrhizal fungi, but the responses are uneven and context-dependent. Warming appears to produce more variable outcomes in ectomycorrhizal fungi than in arbuscular mycorrhizal fungi. Researchers have speculated that mycorrhizal fungi could buffer plants against extinction risk by helping them tolerate changing conditions, or alternatively could either help or hinder plant dispersal into new habitats.21PubMed. Climate change influences mycorrhizal fungal-plant interactions, but conclusions are limited by geographical study bias
A meta-analysis focusing specifically on the mutualism between arbuscular mycorrhizal fungi and plants found that warming from past to present temperatures strengthened the growth benefits wild plants got from their fungal partners. Forecasted future warming may produce modest additional positive effects. Interestingly, rising carbon dioxide levels appeared to have little effect on the mutualism in either direction, which was unexpected given that higher carbon dioxide generally boosts plant growth. The researchers also found that domesticated crop plants responded differently from wild species: the warming boost in mycorrhizal benefit was significant only for wild plants, not crops.22PubMed Central. A meta-analysis of the effects of climate change on the mutualism between plants and arbuscular mycorrhizal fungi Centuries of selective breeding may have weakened crops’ dependence on fungal partners, leaving them less responsive to changes in the relationship.
Fungal Mycelium as a Replacement for Plant-Based Packaging
The structural properties of both kingdoms are now being exploited together in materials science. Researchers have developed biodegradable molded packaging by growing fungal mycelium through processed cotton plant biomass. The mycelium acts as a natural binder, weaving through the plant fibers and producing a composite material. In testing, certain blends of cotton byproducts colonized by fungi met or exceeded the performance characteristics of extruded polystyrene foam, the petroleum-based material used in disposable packaging.23Academia.edu. Fungal Mycelium and Cotton Plant Materials in the Manufacture of Biodegradable Molded Packaging Material: Evaluation Study of Select Blends of Cotton Byproducts The approach leans into what each kingdom does well: plants provide the structural fiber and fungi provide the living glue that binds and shapes it. Several companies have since scaled this concept into commercial products for insulation, packaging, and even leather alternatives, turning two of biology’s oldest manufacturing strategies into an industrial process.