Why Do Mushrooms Not Have Green Leaves?


Mushrooms are once believed to be plants. It was an arbitrary decision several botanists made due to the flaws in the former two-kingdom classification system by Carl Linnaeus. One clear distinction between mushrooms and plants is that the former doesn’t have green leaves.

Mushrooms don’t have green leaves because they are fungi. They lack chlorophyll which is the green pigment of plants. At the same time, mushrooms are the “fruiting bodies” of a fungus. Hence, they don’t have leaves.

This article will discuss the mushroom’s biological background and explain the lack of green leaves. I’ll also clear up some confusion about the so-called ‘mushroom plant’.

Mushrooms Are Fungi, Not Plants

For a long time, the field of biology adhered to the two-kingdom classification system attributed to the Swedish botanist Carl Linnaeus. According to his classification, living organisms are divided into two: Kingdom Plantae and Kingdom Animalia

Linnaeus based the division of the two kingdoms on their feeding mechanism and capability for movement. Organisms under the plant kingdom were categorized as rooted and able to produce food through photosynthesis

On the other hand, the animal kingdom was differentiated due to its motility and food intake. Unlike plants, they cannot produce food and consume plants or other animals to survive.

Carl Linnaeus’ two-kingdom classification was adopted in biology for centuries. For this reason, he was called the “Father of Modern Taxonomy.”

Now, with the plant-animal dichotomy, fungi were classified as plants although they don’t photosynthesize. It could be because they are rooted. However, scientists began to critique this arbitrary assignment of fungi in the plant-animal classification — which is indeed arbitrary given that DNA comparisons show that fungi and animals are more related than plants. 

One of the scientists who raised concerns about the two-kingdom classification system was Robert Whittaker, an American plant ecologist. For him, fungi don’t fit any characteristics of plants and animals.

Fungi were something in between plants and animals and blurred the distinction between the plant-animal dichotomy. The same misfit can be said of other living organisms such as bacteria, algae, and protozoans. To solve this problem, he proposed the five-kingdom classification system.

Fungi Under the Five-Kingdom Classification System

In 1969, Whittaker proposed the following kingdoms as part of a new classification system. This replaced the dichotomy proclaimed by Linnaeus. 

  • Monera
  • Protista
  • Animalia
  • Plantae
  • Fungi

The mentioned kingdoms are differentiated through nutrition, cell organization, respiration, reproduction, and movement. This five-kingdom classification system is still being used today after its publication in the late 20th century. 

Under this new system, fungi are now a kingdom of their own mainly for two reasons: lack of chloroplasts and absorption as their nutritive mechanism.

Fungi Do Not Have Chloroplasts

The chloroplast is the plant organelle that is in charge of photosynthesis. It contains the chlorophyll or the pigment responsible for the plant’s distinctive green color.

Through chlorophyll, a plant involves itself in the process of photosynthesis, where it gathers light energy, usually coming from the sun. Once done, the light will be converted into energy-storing molecules, which the plant will utilize in photosynthesis. The process will begin right after, and the energy will transform carbon dioxide and water into glucose.

The plant will then use the glucose with other nutrients from the soil in the production of leaves and other plant parts. Because of this food-producing mechanism of plants to feed themselves, they are classified as autotrophs. On the flip side, animals consume plants or other animals, which is why they are called heterotrophs

Fungi don’t have chloroplasts, making them incapable of carrying out photosynthesis. Without photosynthesis, they can’t produce their food and have to rely upon some other organic matter to consume. Ultimately, without chloroplasts, they also lack a generally green color.

Fungi Have an Absorptive Feeding System

Fungi don’t have roots. Instead, they have mycelium or thread-like structures buried under the soil or under other organic matter that acts like the roots of a fungus. Mycelium is used by fungi to collect nutrients. This makes absorbing nutrients from any dead or decaying matter easy. 

This feeding mechanism is absorptive. This means that fungi digest their food externally by releasing digestive enzymes to their outside environment. This trait distinguishes fungi from other living organisms.

Mushrooms Are the “Fruit” of Fungi

All mushrooms are fungi, but not all fungi are mushrooms. This is important to remember as there are other organisms under the fungi kingdom, which are yeasts, rusts, smuts, mildews, and molds. 

Mushrooms are the “fruit” part of certain fungi species that grow above the ground. The mycelium, or its roots, on the other hand, is deeply rooted beneath the soil. The mushroom serves as the fungi’s reproductive organ, which disperses spores through wind, water, or insects to multiply. 

Above the ground, the structure of a mushroom is pretty fleshy. It consists of four main parts

  • Cap. This is an umbrella-like structure that varies in color, shape, and size. 
  • Underside. This can be found directly underneath the cap, where you can find either gills, teeth, ridges, or pores. These structures can be a determinant of whether or not a mushroom is poisonous.
  • Stem. This structure supports the cap and is often stiff and woody.  
  • Spores. Mushroom spores are the ones responsible for reproduction through dispersion.

Underground, the mycelium act like roots that absorb nutrients and water from the earth and keep them anchored. Aside from these mentioned parts, mushrooms do not have leaves with them. 

Since these mushrooms are the fruit of a fungus, they can be used in a variety of ways if they’re not poisonous. If cultivated, they can be edible and are used for cooking. Other mushrooms are also utilized for medicinal purposes because of their health benefits.

This video extensively dives into different mushroom structures and how to distinguish them from each other. 

Mushrooms as Saprophytes 

As mentioned, plants are autotrophs, while animals are heterotrophs because of how they produce or consume food. Aside from these modes of nutrition, there are also the saprophytic or saprotrophic ones to which fungi belong. 

Saprotroph is the more technical term for organisms that absorb nutrients from dead and decaying organisms. They release chemicals into an organic matter which helps them decompose it. Fungi will then convert the absorbed complex organic substrates to simpler nutrients.

As I have discussed in another article, mushrooms can be beneficial and detrimental to nearby plants. Mushroom growth around a tree, for example, indicates that the soil is rich in nutrients and of good quality.

However, problems arise when mushrooms start to grow on tree trunks and roots. Mushrooms can be a symptom of severe fungal tree disease. 

Mushrooms on trees infect the tree, causing rot on the sapwood and heartwood of the tree trunk. At this point, even removing mushrooms will not save the tree, and slowing down the decay can only be a viable action.

Rungia klossii or the ‘Mushroom Plant’

Maybe once in your life, you have already heard of the ‘mushroom plant.’ You might think some species of mushroom-producing fungus have green leaves, but now that you have reached this point in the article, you are confused if mushrooms don’t have green leaves. How come there is such a thing called a mushroom plant?

To clear things up, the mushroom plant, or Rungia klossii, is not a fungus. It is a fast-growing herb with thick, glossy, and dark green leaves native to Papua New Guinea. The shrub was called the mushroom plant for its mushroom-flavored leaves, which are recommended for those who are allergic to fungus but love the taste of a mushroom.

Conclusion

Mushrooms are not plants. They are the fruiting body of a fungus that grows above the soil. Through mushrooms, certain species of fungi reproduce themselves.

These toadstools don’t have any leaves and lack chloroplasts that contain green pigment. The mere fact that they are fungi means they are incapable of producing green leaves. Unlike plants which perform photosynthesis internally, mushrooms digest their nutrients externally by releasing digestive enzymes through their mycelium.

Furthermore, one must not be confused with a mushroom plant as it is just an herb and not a fungus. 

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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