No, plants are not poikilotherms. Poikilotherms are animals that have a variable internal body temperature that changes with the environment. Plants don't have a body temperature in the same way animals do, so the term poikilotherm doesn't apply to them. However, plant metabolism is strongly influenced by surrounding temperature, much like poikilothermic animals.
What Does Poikilotherm Mean?
A poikilotherm is an animal whose internal body temperature varies with the temperature of its surroundings. The word comes from Greek:
poikilos meaning "varied" and
therme meaning "heat." Common examples of poikilotherms are reptiles, amphibians, fish, and insects. These animals are often called "cold-blooded," though that's not a precise scientific term. Unlike warm-blooded animals (endotherms) like mammals and birds, poikilotherms don't use metabolic energy to keep a constant body temperature. Instead, they rely on behavioral adaptations—basking in the sun, moving to shade, or burrowing—to adjust their temperature.
Are Plants Poikilotherms? The Straight Answer
Strictly speaking,
plants are not poikilotherms because the term applies only to animals. Plants are a separate kingdom of life. They don't have a central nervous system, blood, or organs dedicated to temperature regulation. A plant's cells respond to the temperature around them, but there is no "body temperature" to measure. That said, scientists sometimes use the word "poikilothermic" loosely to describe any organism whose metabolic rate depends on external temperature—and plants definitely fit that description. So while it's not accurate to call a plant a poikilotherm, it's fair to say plants are
thermally conforming organisms. Their internal temperature is nearly the same as the surrounding air or soil.
How Do Plants Respond to Temperature Changes?
Plants are highly sensitive to temperature. Their enzymes, photosynthesis rate, and growth all speed up or slow down as the thermometer moves. For example, in warm weather, a plant might grow leaves faster, but if it gets too hot (above 100°F for many species), enzymes can denature and the plant stops growing. In cold weather, metabolic processes slow to a crawl. This is why many plants go dormant in winter. Unlike a lizard that moves to a sunlit rock, a plant has no choice—it must cope with whatever temperature comes. Some plants have adaptations like thick leaves, waxy coatings, or hairs to reduce heat loss or protect from frost. Others produce antifreeze proteins that keep cells from freezing.
Do Plants Have a Body Temperature?
Plants don't have a core body temperature like a dog or a human. But parts of the plant can be slightly different from the air temperature. Leaves, for instance, can heat up in direct sunlight or cool down when water evaporates from their surface (transpiration). A leaf can be several degrees warmer or cooler than the air. The same goes for roots, which are insulated by the soil. Scientists measure leaf temperature with infrared thermometers or thermal cameras. During a hot day, a leaf might be 10°F cooler than the surrounding air if it is transpiring heavily. So while a plant doesn't regulate temperature internally, it does influence the temperature of its own tissues through physical processes.
Can Plants Regulate Their Internal Temperature?
For most plants, the answer is no—they cannot actively generate heat to warm themselves. However, there is a fascinating exception:
thermogenic plants. These are plants that can produce heat metabolically. The most famous example is the skunk cabbage (Symplocarpus foetidus), which can raise the temperature of its flower to about 70°F even when the air is freezing. This heat helps to melt snow around the plant and attract pollinators. Another example is the voodoo lily (Amorphophallus konjac), which heats up to spread its foul odor. These plants use a specialized metabolic pathway (cyanide-resistant respiration) to generate heat. But even these plants are not thermoregulating like a mammal—they heat up temporarily and then cool down. So, except for a few rare species, plants do not actively regulate their temperature.
Are Plants Cold-Blooded?
The term "cold-blooded" is commonly used for animals like snakes and frogs. It's not a scientific term for any type of organism. Using it for plants is confusing because plants don't have blood. A better description is that plants are
temperature-dependent in their biological functions. They are ectotherms in the broad sense (heat comes from outside), but they don't have a body temperature that swings between hot and cold. If you say "plants are cold-blooded" in casual conversation, most people will understand you mean they are affected by the temperature around them. But for accurate science writing, avoid the term entirely.
How Does Temperature Affect Plant Growth?
Temperature influences almost every stage of a plant's life. Here are the key effects:
-
Seed germination: Seeds require a specific temperature range to sprout. Too cold, and they stay dormant. Too hot, and they die.
-
Photosynthesis: The chemical reactions in chloroplasts work fastest at moderate temperatures (usually 60–85°F for most garden plants). Beyond that, efficiency drops.
-
Respiration: Plants burn sugars for energy. Respiration increases with temperature, sometimes faster than photosynthesis, which can deplete energy stores.
-
Transpiration: Water loss through leaves speeds up in hot, dry conditions, which can stress the plant.
-
Growth rate: In general, plant cells expand faster in warmth. That's why spring and summer are active growing seasons.
-
Flowering and fruiting: Many plants need a period of cold (vernalization) or a specific temperature trigger to bloom. For example, tulips need a cold winter before they flower in spring.
The following table gives a simple comparison between how typical land plants and typical poikilothermic animals handle temperature:
| Aspect | Typical Poikilothermic Animal (e.g., lizard) | Typical Land Plant |
|--------|-----------------------------------------------|---------------------|
| Temperature source | Absorbed from environment | Absorbed from environment |
| Body temperature | Changes with surroundings; can move to regulate | Tissue temperature changes with surroundings; cannot move |
| Active regulation | Behavioral (basking, hiding) | Structural (waxy leaves, transpiration cooling) |
| Internal heat generation | Very limited (mostly from digestion) | Rare (thermogenic plants) |
| Core temperature concept | Yes, internal organs have temperature | No core; all parts vary locally |
For home gardeners, understanding temperature effects is crucial. A simple tool like a
soil thermometer can help you know when to plant seeds. If you want to start seeds indoors, a
heat mat can keep soil at the ideal temperature for germination. A good
digital temperature and humidity monitor can track conditions in a greenhouse or grow room. Books on plant physiology also dive deeper into how plants respond to heat and cold.
Check out soil thermometers on Amazon
Find seedling heat mats on Amazon
Browse temperature monitors on Amazon
What About Aquatic Plants?
Water temperature changes more slowly than air temperature, so aquatic plants experience a more stable environment. But they are still not poikilotherms because they are plants, not animals. Their metabolic rates adjust to water temperature. Some aquatic plants, like certain algae, can survive extreme temperature ranges because their cells contain protective compounds. The same principles apply: no internal temperature control, just adaptation.
Does the Term Poikilotherm Apply in Any Context to Plants?
You might see the phrase "poikilothermic plants" in older or informal scientific writing. Some researchers have used it to describe how plants' metabolic rates vary with temperature. But modern biology reserves the term for animals. In fact, some authors have suggested using the word
poikilohydric for plants that lack control over their internal water content (like mosses and lichens). That's a separate concept. If you encounter "poikilothermic plant," understand the speaker is making a loose analogy, not stating a fact.
How Does Plant Temperature Research Help Gardeners?
Understanding that plants are not poikilotherms but are temperature-sensitive helps you make better gardening decisions. Check soil temperature before planting seeds in spring. Use
row covers or
cold frames to buffer temperature swings. Mulch around roots to keep soil cool in summer and warm in winter. Water plants in the morning so they can transpire during the heat of the day. If you grow tropical plants indoors, keep them away from drafty windows and heating vents. Knowing that a plant's internal processes depend on external temperature means you can create a more stable growing environment for healthier plants.
What Are Common Misunderstandings About Plants and Temperature?
One big myth is that plants "sweat" to cool themselves. They do transpire water, which cools the leaves, but it's passive, not controlled like sweating in mammals. Another myth is that plants can "feel" cold and move away. They don't have nerves or muscles. A third confusion is that plants hibernate like animals. Dormancy is not the same as hibernation; it's a state of reduced metabolic activity triggered by light and temperature, not voluntary.
To wrap up, remember:
plants are not poikilotherms because they aren't animals. But they share the key trait of poikilotherms—their biological rate is tied to environmental temperature. Learning how plants cope with heat and cold can make you a better plant caregiver, whether you're growing tomatoes in your backyard or caring for a houseplant.
