Three Reasons Fungi Are Not Plants
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Three Reasons Fungi Are Not Plants
Three Reasons Fungi Are Not Plants
Brian Lovett, Ph.D.
Published: Jan. 6, 2021
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Have you ever picked up something and wondered, "what is that?" Taxonomists help answer that question by dutifully documenting phenotypic (trait) and genotypic (genetic) differences among living things that allow them to be quickly distinguished and identified. Placing organisms into categories is useful so that instead of describing a slew of characteristics, we can simply use broad categories as reference points to inform us not only about the nature of an individual, but also about its relationship to other similar organisms. A new organism classified as a vertebrate, for example, will be commonly understood to have a spine composed of vertebrae. For scientists, taxonomic groups are touchstones of understanding: a foundation upon which to build new knowledge. This metaphor communicates the fundamental importance of taxonomy, but it implies a stability that taxonomic classification lacks.
For much of scientific history, fungi have been a botanist's domain. Until very recently — reasonably within a human lifetime — fungi remained classified as plants as part of a centuries-old division that can be summed up by an axiom attributed to Carl Linnaeus: "Plants grow and live; Animals grow, live and feel." This "father of modern taxonomy" (and deviser of racist classifications of humans) classified living organisms into 2 categories: either animals or plants. This paradigm can be rephrased as animals and "not animals," as the category "plants" long represented a ragtag group of unrelated organisms. Without the context of evolution, these classifications sought to place organisms by perceived, oberservable similarity, instead of "relatedness" in a modern, genetic sense.
Classifying fungi as plants has led to some curious events. The earliest description of fungi pathogenic to insects (likely Cordyceps militaris) by the French entomologist René Antoine Ferchault de Réaumur was as a plant root. The Mycological Society of America was established while fungi were still considered plants, and the society's journal Mycologia originated from the New York Botanical Garden. This garden continues to maintain one of the world's largest collections of fungi in their herbarium. This pairing of fungi with plants is a present problem: misclassification matters because how we classify organisms affects how we understand, support (financially and culturally) and engage with them.
Why Were Fungi Ever Considered Plants?
Today, we know that fungi are not plants, but the botanical history of fungi provides an interesting perspective on our scientific biases, on how we classify organisms and how these impact our collective knowledge.
Taxonomic classifications are in constant flux, as we refine our understanding of the incredible diversity that surrounds us. Even in the age of genomics, we have only just scratched the surface of this diversity. Because we don't have a full picture of the diversity of life, our best laid classifications can be (and are) routinely shifted by a newcomer or fresh evidence. Today, we have the luxury of molecular tools for classification, but taxonomic classifications can be traced back before the discovery of DNA, the concept of evolution and the invention of the microscope. Early classifications were limited by the tools (and views) available to them.
We must keep this caveat in mind when examining some of the early attempts at classifying life. Mushrooms were the earliest representatives of fungi to be classified. Based on observations of mushrooms, early taxonomists determined that fungi are immobile (fungi are not immobile) and they have rigid cell walls that support them. These characteristics were sufficient for early scientists to determine that fungi are not animals and to lump them with plants.
Reason 1: Fungi Lack Chloroplasts
Ghost pipes are an example of plants that lost chlorophyll. They obtain nutrients by parasitizing fungi (mycoheterotrophic).<br>Source: iStock
We have arrived at our first reason fungi are not plants: fungi lack chloroplasts. This verdant, unifying feature of plants is readily observable to the eye, and these chlorophyll-containing plastids continue to be an important milestone for our modern understanding of plant evolution. Of course, there are plants that lack functional chloroplasts, such as ghost pipes (Monotropa), but we know these flowering plants ("higher plants," once upon a time) lost chlorophyll during their evolutionary history. This evolutionary context was lacking until Darwin came along, but demonstrates how callously uncooperative biology is with our artificial delineations. Broad outlines for our categories for living things were based on what we could see, and microbes, including fungi without a fruiting body to observe, were an...