Most plants photosynthesize, but hundreds of species have partially or completely abandoned the process. Some steal nutrients directly from neighboring plants, others siphon carbon from underground fungal networks, and a few blend both strategies depending on how much light they can get. The familiar rule that plants make their own food from sunlight is a strong generalization, not an absolute law, and the exceptions turn out to be more varied and more common than most people realize.
Plants That Steal From Other Plants
The most dramatic departure from photosynthesis occurs in parasitic plants. Rather than capturing sunlight, these species tap directly into the tissues of a host plant and draw water, sugars, and minerals from it. They accomplish this through specialized structures called haustoria, which physically invade the host’s roots or stems and connect to its vascular system, essentially hijacking the plumbing that the host built for itself.1PubMed. Developing for nutrient uptake: Induced organogenesis in parasitic plants and root nodule symbiosis The result is a plant that can grow, flower, and set seed without ever producing a single sugar molecule on its own.
Some parasitic plants still retain a bit of green tissue and do a small amount of photosynthesis alongside their parasitism. These are called hemiparasites, and mistletoe is one of the most familiar examples. But others have gone all the way. The family Balanophoraceae consists entirely of species that have lost the ability to photosynthesize. They look nothing like a typical plant: often fleshy, pale, or reddish lumps emerging from the forest floor, entirely dependent on their host for energy.2PubMed Central. Genomic comparison of non-photosynthetic plants from the family Balanophoraceae with their photosynthetic relatives Another well-known group is the broomrapes (genus Orobanche and its relatives), which are completely lacking in chlorophyll and parasitize crop roots underground, often without any visible aboveground sign until they flower.3PubMed Central. Broomrape Weeds. Underground Mechanisms of Parasitism and Associated Strategies for their Control: A Review
Plants That Feed Through Fungi
Parasitic plants target other plants, but a separate group of non-photosynthetic species takes a less direct route: they exploit fungi. These are called mycoheterotrophs, and they get their carbon by tapping into the underground fungal networks (mycorrhizae) that connect most forest trees and shrubs. In effect, a tree photosynthesizes and shares some of its sugars with a fungal partner in the soil. The mycoheterotrophic plant then taps into that same fungal network and draws off carbon without contributing anything in return.
The Indian pipe (Monotropa uniflora) is a classic example. It is ghostly white, completely devoid of chlorophyll, and grows in deep forest shade where photosynthesis would barely be possible anyway. Despite looking more like a fungus than a plant, it is a true flowering plant with roots, stems, and seeds. Carbon transfer through shared mycorrhizal networks has been documented in forests for decades, and the architecture of these underground connections turns out to be more extensive than researchers once assumed.4PubMed Central. Belowground carbon transfer across mycorrhizal networks among trees: Facts, not fantasy Full mycoheterotrophs are essentially freeloaders on this system.
Researchers can now distinguish mycoheterotrophs from normal photosynthetic plants by examining the fatty acids in their tissues. As a plant becomes more dependent on fungal carbon, its fatty acid profile shifts: it starts to look less like a self-feeding plant and more like the fungus supplying it. Specifically, one fatty acid associated with fungi becomes more abundant as mycoheterotrophic dependence increases, while a fatty acid common in photosynthetic tissue declines.5PubMed Central. Fatty acid signatures distinguish autotrophy, partial mycoheterotrophy, and full mycoheterotrophy in angiosperms This chemical fingerprint helps botanists figure out which species are secretly cheating and which are genuinely making their own food.
The Gray Area Between Self-Feeding and Freeloading
The split between photosynthetic and non-photosynthetic is not always clean. Many species sit somewhere in the middle, doing some photosynthesis but also pulling carbon from fungi. These partially mycoheterotrophic plants have green leaves, grow in shaded environments, and appear to supplement their photosynthetic income with fungal carbon when light levels drop. Certain orchids are good examples. The orchid Cheirostylis liukiuensis grows in low-light forest understory and has reduced underground organs, both features that hinted it might be partially mycoheterotrophic. Analysis of its fungal partners and tissue chemistry confirmed it: the plant gets a meaningful share of its carbon from fungi in the soil rather than from its own leaves.6Plant Species Biology. Partial mycoheterotrophy in rhizoctonia‐associated orchid Cheirostylis liukiuensis
This kind of mixed strategy may be far more common than the textbook picture suggests. A plant does not have to be white and leafless to cheat the system. Some green, leafy orchids in temperate forests get a surprisingly large fraction of their carbon from underground fungal partners, even though they look perfectly capable of photosynthesizing on their own. The ratio shifts depending on how much light is available, almost like a dimmer switch between self-sufficiency and dependence.
Orchid Seeds and the Earliest Stage of Life Without Light
Even orchids that photosynthesize perfectly well as adults start life as complete freeloaders. Orchid seeds are tiny, dust-like, and contain essentially no energy reserves of their own. To germinate in the wild, they must be colonized by specific mycorrhizal fungi that provide the carbon the seedling needs to grow its first leaves. Without the right fungal partner, the seed simply never develops.7PubMed. Orchids acquire fungal carbon for seed germination: pathways and players This means that tens of thousands of orchid species, from tropical epiphytes to northern bog orchids, all pass through a stage where they survive without any photosynthesis at all. It is one of the reasons orchids are notoriously difficult to grow from seed in captivity.
This early-life dependence on fungi also helps explain why full mycoheterotrophy has evolved so many times in the orchid family. The machinery for extracting carbon from a fungal partner is already there in the seed. All that needs to happen, evolutionarily speaking, is for the plant to keep relying on that fungal connection instead of building functional photosynthetic leaves as it matures. Once that transition begins, evolution tends to push it further, because maintaining the complex molecular machinery for photosynthesis is expensive if the plant is not using it.
What Happens to the Genome When Photosynthesis Disappears
Photosynthesis requires a large set of genes, many of which are carried in the chloroplast (the organelle where photosynthesis happens). When a plant lineage stops photosynthesizing, those genes start to decay. Mutations accumulate in them without consequence because the genes are no longer needed, and over time, the genes are deleted entirely. In Balanophoraceae, researchers found extensive loss of photosynthesis-related genes in the plastid genome.2PubMed Central. Genomic comparison of non-photosynthetic plants from the family Balanophoraceae with their photosynthetic relatives The same pattern shows up in parasitic broomrapes: their plastid genomes have shrunk dramatically, and the genes that remain have evolved at an unusually fast rate compared to their photosynthetic relatives.8PubMed. Evolution of plastid gene rps2 in a lineage of hemiparasitic and holoparasitic plants: many losses of photosynthesis and complex patterns of rate variation
This genomic erosion is essentially a one-way street. Once a plant has lost enough photosynthesis genes, there is no practical way to rebuild the system. The degradation is slow enough that transitional stages exist: some hemiparasitic species retain a partial set of photosynthesis genes and can still photosynthesize weakly, while their fully parasitic relatives in the same family have lost them almost completely. These transitional lineages give researchers a time-lapse view of how a plant evolves away from self-feeding.
Interestingly, even plants that have thoroughly abandoned photosynthesis tend to keep their plastids. The organelle still serves other functions, including synthesizing certain amino acids and fatty acids, so it persists in a stripped-down form even after its signature job is gone. The non-photosynthetic broomrape Phelipanche, for example, still carries plastid genes, and researchers have even found evidence of horizontal gene transfer between different broomrape genera, where one parasitic plant apparently acquired a plastid gene from another.9Molecular Phylogenetics and Evolution. Horizontal gene transfer of a plastid gene in the non-photosynthetic flowering plants Orobanche and Phelipanche (Orobanchaceae)
Carnivorous Plants Still Photosynthesize
A common misconception is that carnivorous plants like Venus flytraps and sundews have replaced photosynthesis with insect-eating. They have not. Every carnivorous plant photosynthesizes. The insects and other prey they capture provide supplemental nutrients, primarily nitrogen and phosphorus, that are scarce in the boggy, nutrient-poor soils where most carnivorous species grow. The traps themselves are modified leaves, and those modified leaves tend to have lower photosynthetic rates than the plant’s non-trap foliage because their structure has been reshaped for capturing prey rather than absorbing light.10PubMed Central. Spatio-temporal changes of photosynthesis in carnivorous plants in response to prey capture, retention and digestion But the plant’s ordinary leaves carry on photosynthesizing as usual.
So carnivory in plants is not an alternative to photosynthesis; it is a nutritional supplement layered on top of it. This is fundamentally different from parasitism or mycoheterotrophy, where the plant is replacing photosynthetic carbon with carbon from another organism. A Venus flytrap grown in good light and given mineral fertilizer can do perfectly well without ever catching a fly. It just grows better and reproduces more successfully if it gets the extra nutrients from prey.
How Parasitic Plants Find Their Hosts Underground
One of the more remarkable aspects of non-photosynthetic parasitic plants is how they locate a host in the first place. Root-parasitic species like broomrapes spend their early life underground as tiny seeds in the soil. They cannot afford to germinate randomly, because without photosynthesis they have no way to sustain themselves if they miss a host root. Instead, they wait for a chemical signal. Host plants naturally release compounds called strigolactones from their roots, and parasitic seeds have evolved receptors that detect these molecules and trigger germination only when a host is close enough to reach.11PubMed Central. A New Series of Strigolactone Analogs Derived From Cinnamic Acids as Germination Inducers for Root Parasitic Plants
The effective signaling distance is surprisingly short and depends heavily on soil conditions. In experiments measuring how far a synthetic strigolactone could travel through different soils, the germination-triggering range varied from a fraction of a millimeter in clay soil to around 14 millimeters in coarser sand. Soil microbes also matter: sterilizing the soil increased signaling distances, suggesting that soil bacteria normally break down the signal before it travels far.12PubMed. Soil-dependent variation in strigolactone signaling distance revealed by a parasitic seed germination bioassay This means a parasitic seed might sit dormant in the soil for years until a host root grows within a centimeter or so of it. The precision of this system is both elegant and, for farmers, deeply frustrating.
Why Non-Photosynthetic Plants Matter for Agriculture
The agricultural damage from parasitic plants is serious, and broomrapes are among the worst offenders. Species like Orobanche and Phelipanche attack crops including tomatoes, sunflowers, fava beans, and carrots across the Mediterranean, central and eastern Europe, and large parts of Asia. Because the parasite operates entirely underground during the critical early stages of infection, and because it physically merges with the host’s vascular system, conventional weed-control strategies designed for surface-growing weeds are largely useless.3PubMed Central. Broomrape Weeds. Underground Mechanisms of Parasitism and Associated Strategies for their Control: A Review
Researchers have explored a wide range of unconventional approaches. One promising concept is “suicidal germination”: applying synthetic strigolactone analogs to the field to trick parasitic seeds into germinating when no host is present, so they exhaust their energy reserves and die. Other strategies target different stages of the parasite’s lifecycle, from reducing seed-bank viability through soil fumigation or solarization, to breeding crop varieties with natural resistance to haustorial penetration, to delivering herbicides directly through the haustorial connection after the parasite has attached. Even allelopathic compounds from eucalyptus trees have shown potential to inhibit broomrape seed germination in laboratory settings.13Indian Journal of Weed Science. Allelopathic potential of Eucalyptus camaldulensis Dehnh. on germination of obligate root-parasitic broomrape (Orobanche cernua loefl.) No single method has proven decisive, and integrated approaches combining several tactics are the norm.
Photosynthesis in Unexpected Places
While some plants have given up photosynthesis entirely, others carry it out in places you might not expect. Many trees and shrubs photosynthesize through their bark, particularly species with thin, greenish bark like aspens and birches. In aspen, bark photosynthesis can meaningfully contribute to the carbohydrate supply of the stem during periods when the tree has no leaves, such as early spring before leaf-out or after autumn leaf drop.14Forest Science. The Contribution of Aspen Bark Photosynthesis to the Energy Balance of the Stem Fruit peels, flower sepals, and even the green surfaces of some seed pods can also photosynthesize to a small degree.
This is worth knowing because it complicates the simple mental model of “leaves do photosynthesis, everything else does not.” In reality, any plant tissue containing chlorophyll can capture some light energy, and many species exploit this in tissues beyond their leaves. It does not mean bark is as efficient as a leaf at photosynthesis, but in a leafless deciduous tree, even a modest contribution from the bark helps offset the carbon the stem loses to respiration during dormancy. For the tree, it is a bit like having a small backup generator running when the main power plant is offline.
Non-Photosynthetic Algae and What They Tell Us About Plants
Plants are not the only photosynthetic organisms that have sometimes evolved away from photosynthesis. Among the green algae, the group from which land plants descended, there are lineages that have independently abandoned photosynthesis multiple times. The colorless green algae Prototheca and Helicosporidium still possess plastids, but those plastids have lost the genes needed for photosynthesis. Phylogenetic analysis suggests that photosynthesis was lost independently at least three times within this single clade.15PubMed Central. Multiple losses of photosynthesis and convergent reductive genome evolution in the colourless green algae Prototheca And even in these non-photosynthetic algae, certain electron transport components originally associated with photosynthesis persist in the plastid, likely repurposed for other biochemical tasks.16PubMed Central. A non-photosynthetic green alga illuminates the reductive evolution of plastid electron transport systems
These algal examples reinforce a broader point: losing photosynthesis is not a one-off evolutionary curiosity. It has happened repeatedly across the tree of life whenever an organism finds a reliable alternative source of carbon. In land plants, that alternative is usually another plant (via parasitism) or a fungus (via mycoheterotrophy). In algae, it can be absorbing dissolved organic matter from the environment. The pattern is consistent: once an organism can get its carbon cheaply from somewhere else, the expensive molecular machinery of photosynthesis begins to erode, gene by gene, generation by generation, until the process is gone for good.