Most lichens grow between a fraction of a millimeter and a few millimeters per year, making them some of the slowest-growing visible organisms on Earth. A thumbnail-sized patch on a rock could easily be a decade old, and some large colonies in harsh environments have been accumulating for centuries. But the actual pace varies wildly depending on species, growth form, and where the lichen lives, with measured rates spanning roughly a thousandfold range across different settings.
Why Lichens Are So Slow
Lichens are not a single organism but a partnership between a fungus and one or more photosynthetic partners, usually a green alga or cyanobacterium. The photosynthetic partner makes sugars from sunlight, and the fungus provides structure and protection. This arrangement is remarkably tough, allowing lichens to colonize bare rock, tree bark, and soil in places where most plants cannot survive. The trade-off is speed. Unlike a plant with roots drawing constant water from the soil, a lichen can only photosynthesize when its body is wet. In dry conditions, it essentially shuts down and waits.
This dependence on external moisture is the single biggest reason lichens grow slowly. Researchers have long recognized that lichens are “poikilohydric,” meaning their internal water content tracks whatever the environment provides rather than being actively regulated. Photosynthetic production is mainly determined by water availability, and in extreme environments the very presence of lichens reflects the existence of a reliable external water supply.
Even in a wet climate, a lichen is not growing around the clock. A study of the foliose lichen Lobaria pulmonaria in a high-rainfall oceanic environment found that growth at a monthly scale was positively related to time the lichen spent hydrated while exposed to light. Time spent wet in the dark, by contrast, was actually associated with slower growth, because the lichen burns through stored sugars via respiration without producing new ones through photosynthesis.1PubMed Central. Interactions of moisture and light drive lichen growth and the response to climate change scenarios: experimental evidence for Lobaria pulmonaria So the window for real growth is narrower than you might think: the lichen needs to be simultaneously wet and sunlit.
How Fast Different Lichens Actually Grow
Growth rates differ dramatically depending on a lichen’s growth form. Crustose lichens, the ones that form thin, paint-like crusts glued tightly to rock surfaces, tend to be the slowest. Foliose lichens, which have leafy lobes lifted slightly off the surface, grow faster. Fruticose lichens, the shrubby or hair-like types that dangle from tree branches or stand upright on soil, can be faster still.
To put real numbers on this: a 20-year study of the crustose lichen Haematomma erythromma on Elephant Island, Antarctica, measured radial growth of just 0.2 to 0.7 mm per year across 178 individual thalli, making it one of the slowest Antarctic lichens recorded.2Oecologia Australis. Growth Rate and Behavior Over 20 Years in the Crustose Lichen Haematomma erythromma at Elephant Island, Antarctica At the other end of the scale, some foliose species in temperate forests can manage several millimeters per year, and a theoretical upper limit for radial growth has been estimated at roughly 26 mm per year based on the rate at which carbon dioxide can diffuse to the lichen’s edge.3PubMed Central. A universal growth limit for circular lichens Few lichens in nature come anywhere close to that ceiling.
In alpine and polar settings, where conditions are harshest, the numbers drop to almost unbelievable lows. Experiments tracking the crustose lichen Rhizocarpon superficiale in the Colorado Front Range found a maximum radial growth rate of just 0.016 mm per year. By comparison, Xanthoparmelia coloradoensis in the same study grew at about 2 mm per year once it reached a certain size, more than a hundred times faster.4BioOne Complete (Arctic, Antarctic, and Alpine Research). Experiments on Lichen Growth, III. The Shape of the Age-Size Curve At 0.016 mm per year, a lichen would take more than 60 years to grow a single millimeter in radius. That is not a typo.
The Antarctic Growth Cline
Antarctica provides a dramatic natural experiment in how climate controls lichen growth. A study spanning 51 years at Cape Hallett in Northern Victoria Land measured mean growth rates of about 0.068 mm per year for the crustose species Buellia frigida and about 0.090 mm per year for Rusavskia elegans.5Polar Biology. Lichen growth rates over 51 years at Cape Hallett, Northern Victoria Land, support a large (100x) cline across Antarctica Those are among the slowest growth rates recorded for any organism on the planet.
Yet in the warmer, wetter maritime Antarctic, crustose lichens grow far faster. Buellia latemarginata, a crustose species measured in the maritime Antarctic, grew at 0.87 mm per year, one of the highest rates recorded for crustose lichens anywhere on the continent.6Environmental Pollution. Slowest to fastest: Extreme range in lichen growth rates supports their use as an indicator of climate change in Antarctica Across the continent as a whole, crustose lichen growth rates show roughly a hundredfold cline, from some of the lowest known rates in the McMurdo Dry Valleys at 78°S to near the fastest at maritime Livingston Island at 63°S. That gradient tracks closely with changes in temperature and precipitation.5Polar Biology. Lichen growth rates over 51 years at Cape Hallett, Northern Victoria Land, support a large (100x) cline across Antarctica
The take-home point is that location matters as much as species when it comes to lichen growth. The same genus can grow ten or a hundred times faster simply by being in a less extreme spot.
Moisture Sources You Might Not Expect
When people think about what keeps lichens wet, rain is usually what comes to mind. But for many lichens, especially in arid regions, dew and fog are more important than rainfall. In the Negev Desert, researchers found that the expansion of crustose lichens was principally determined by dew, while fruticose lichens depended more on fog. Crustose forms intercepted roughly 0.09 mm of moisture during dew events, and both forms collected similar amounts from fog, around 0.15 to 0.16 mm. Fog interception increased substantially with wind speed, which helps explain why shrubby fruticose lichens proliferate in fog-prone coastal areas where wind is common.7PubMed. Dew and fog as possible evolutionary drivers? The expansion of crustose and fruticose lichens in the Negev is respectively mainly dictated by dew and fog
Even in wetter climates, the way moisture reaches the lichen is more nuanced than simple precipitation totals. The Lobaria pulmonaria study mentioned earlier found that lichen hydration was better explained by vapor pressure deficit, essentially how thirsty the surrounding air is, than by how much rain had fallen.1PubMed Central. Interactions of moisture and light drive lichen growth and the response to climate change scenarios: experimental evidence for Lobaria pulmonaria A foggy, humid forest with modest rainfall can be a better environment for lichen growth than a place with heavier but sporadic rain followed by dry, sunny stretches.
Nutrients and Bird Droppings
Lichens get most of their nutrition from the air and from whatever washes over their surface, since they have no roots. This means that nutrient inputs like dust, dissolved minerals in rainwater, and, yes, bird droppings can meaningfully change how fast a lichen grows. Experimental work found that treating the crustose lichen Xanthoparmelia conspersa with bird droppings increased its radial growth. However, the same treatment actually inhibited growth of Parmelia saxatilis, a species that is rarely found on rocks where birds perch.8Springer International. The Influence of Environmental Factors on the Growth of Lichens in the Field
This is a useful reminder that “more nutrients” does not automatically mean “faster growth” for every lichen. Species adapted to nutrient-poor surfaces can actually be harmed by enrichment, while species already common in nutrient-rich spots thrive on it. This is why you often see different lichen communities on rocks below bird perches versus rocks a few meters away: the nutrient regime effectively selects for different species.
How Long Does It Take a Lichen to Get Started?
Before a lichen can grow at any measurable rate, it first has to establish itself on a surface, and this colonization phase has its own timeline. A study tracking early development of Lobaria pulmonaria from tiny vegetative fragments found that anchoring hyphae developed within two to four months after the fragment landed. After 15 months, growth zones had differentiated and small lobes about 0.5 mm wide were visible.9PubMed Central. Ecology of Lichens on Rock Surfaces That is actually fairly quick by lichen standards.
Other species take much longer. In Lobaria scrobiculata and several Platismatia species, at least four years were needed before recognizable juvenile thalli appeared in the field. For L. scrobiculata specifically, the first distinct lobules showed up 29 months into the experiment, and even at the four-year mark the largest lobules were only 0.4 to 1.3 mm across.9PubMed Central. Ecology of Lichens on Rock Surfaces So if you are watching a bare rock and wondering when lichens will appear, the honest answer is somewhere between a few months and several years for the first detectable growth, depending heavily on the species and whether conditions favor establishment.
Growth also is not linear over a lichen’s lifetime. Young lichens typically grow slowly as they establish, then accelerate during a middle phase, and eventually slow again as the colony gets large. The experiments on Rhizocarpon superficiale in Colorado showed a sigmoidal curve: growth accelerated to a maximum rate, then declined as the thallus expanded.4BioOne Complete (Arctic, Antarctic, and Alpine Research). Experiments on Lichen Growth, III. The Shape of the Age-Size Curve This means that applying a single average growth rate to estimate age can be misleading for very small or very large colonies.
Recovery After Fire and Other Disturbances
One of the most practical questions about lichen growth timelines comes up in land management: how long does it take for lichen cover to come back after a disturbance like wildfire? The answer, unfortunately for caribou and reindeer herders, is decades to a century or more.
In northern Sweden, studies of burned areas found that fruticose reindeer lichens, the forage species caribou and reindeer depend on, typically dominate the ground cover at intermediate stages of ecological succession roughly 50 to 100 years after fire.10Ecological Engineering. Restoration of reindeer lichen pastures after forest fire in northern Sweden: Seven years of results In Alaska tundra, a study of burned caribou winter range found even less encouraging results. Extrapolating observed recovery rates forward to 50 years after fire predicted lichen cover of about 4%, compared to the original unburned cover of roughly 16%, and the researchers considered that probably not enough to be usable by caribou.11Arctic, Antarctic, and Alpine Research. Slow Recovery of Lichen on Burned Caribou Winter Range in Alaska Tundra: Potential Influences of Climate Warming and Other Disturbance Factors
These timelines are not just an academic concern. In Scandinavia and northern Canada, reindeer and caribou herders are directly affected by the pace of lichen recovery on burned land. When fire frequency increases, the slow regrowth of forage lichens can shrink the usable range faster than the lichens can bounce back. It is one of the clearest examples of how lichen growth rates have real consequences for ecosystems and the people who depend on them.
Climate Change and Shifting Growth Patterns
Given how sensitive lichens are to moisture and temperature, you might expect climate change to have clear-cut effects on their growth. The picture, though, is messier than a simple “warmer equals worse” story. In Western Europe, more epiphytic lichen species, those growing on trees, appear to be increasing rather than declining as temperatures warm. Many ground-dwelling terricolous species, by contrast, are declining.12Environmental Pollution. Further evidence of the effects of global warming on lichens, particularly those with Trentepohlia phycobionts
An experiment simulating climate change by transplanting high-elevation lichens to lower, warmer elevations found high variability among species. Some responded poorly: Hypogymnia flavida had the worst outcomes, with reduced health. But Dolichousnea longissima actually grew faster, had healthier thalli, and produced more photosynthetic pigments under the warmer, drier simulated conditions. Other species hedged their bets by shifting their life-history strategies, such as producing reproductive structures earlier or trading faster growth for delayed reproduction.13Ecosphere. Simulated climate change impacts health, growth, photosynthesis, and reproduction of high-elevation epiphytic lichens
The underlying variable that matters most seems to be humidity rather than temperature per se. Warmer air holds more moisture before becoming saturated, which raises the vapor pressure deficit and can dry out lichens faster even if rainfall does not change. For species that depend on frequent fog or dew, a small shift in local humidity regimes could be more consequential than a degree or two of warming.
Air Pollution as a Growth Suppressor
While climate change effects on lichens are mixed, the effects of sulfur dioxide pollution are straightforward and negative. Lichens absorb gases directly across their surfaces, and sulfur dioxide is toxic to many species. In urban and industrial areas, sulfur dioxide has historically been a primary driver of lichen population declines, causing morphological damage such as smaller, more compact thalli and reduced coverage on surfaces.14Total Environment Advances. Lichens as effective bioindicators for monitoring environmental changes: A comprehensive review
This sensitivity has actually made lichens useful as biological monitors of air quality. The presence or absence of certain lichen species in an area gives a rough readout of how clean the air is. In many European and North American cities, lichen diversity plummeted during the peak of industrial sulfur emissions in the mid-20th century and has partially recovered as clean air regulations took effect. If you notice more lichen on urban trees than your grandparents remember, cleaner air is probably part of the explanation.
Growing Lichens in the Lab
Researchers who want to study lichen biology or harness their unique chemical compounds face a basic problem: lichens are extremely difficult to grow in laboratory conditions. The fungal partner can often be isolated and cultured on its own, but reconstituting the full lichen symbiosis in a petri dish remains a major challenge. The type of starting material, the composition of the growth medium, temperature, humidity, and light cycles all need to be carefully controlled, and even then growth is slow and unreliable.15PubMed Central. A Review of Laboratory Requirements to Culture Lichen Mycobiont Species
This difficulty has practical consequences. Lichens produce a remarkable array of secondary metabolites, compounds not found in other organisms, some of which have pharmaceutical or industrial potential. But harvesting them from wild populations is unsustainable given how slowly lichens grow, and scaling up production requires lab cultivation methods that do not yet work well. Improving in vitro culture techniques is an active area of research, but for now, the slow pace of lichen growth remains a bottleneck for anyone hoping to use lichen-derived compounds at scale.
Using Lichen Size to Date Surfaces
The slow, relatively predictable growth of certain lichens has been turned into a dating tool called lichenometry. The idea is simple: measure the diameter of the largest lichen on a rock surface, apply a known growth rate for that species and region, and estimate how long the surface has been exposed. Geologists have used this technique to date glacial moraines, rock falls, and other landforms.
The method works best with slowly growing crustose species like Rhizocarpon, whose age-size relationship has been studied at multiple sites. But the sigmoidal growth curve described earlier complicates things. Because growth accelerates during a lichen’s early life and then slows down later, a single linear growth rate applied across all sizes can either overestimate or underestimate age depending on the colony’s size. The Colorado experiments showed that Rhizocarpon superficiale’s radial growth accelerated to a peak rate of 0.016 mm per year and then declined, defining a clear sigmoidal curve.4BioOne Complete (Arctic, Antarctic, and Alpine Research). Experiments on Lichen Growth, III. The Shape of the Age-Size Curve The hundredfold growth rate cline across Antarctica underscores that a growth rate calibrated in one location cannot be blindly applied elsewhere.5Polar Biology. Lichen growth rates over 51 years at Cape Hallett, Northern Victoria Land, support a large (100x) cline across Antarctica
Lichenometry is most reliable when local growth-rate calibrations exist, ideally from surfaces of known age like dated gravestones or historically documented rockfalls. Without that local calibration, estimates can be off by a factor of several. Still, for surfaces hundreds or thousands of years old in remote polar or alpine settings where other dating methods are impractical, lichens remain one of the few available clocks.