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| In early classification systems, these morel mushrooms (Morchella esculenta) were included with plants. |
At one time, morel mushrooms and other fungi were considered plants. That was
when all life was classified as either plant or animal, and morels sure didn’t
look like animals. They emerge from the soil, they don't move, and they produce “fruiting” bodies (mushrooms) for reproduction. In addition, its cells are
surrounded by rigid walls, as are the cells of ferns, grasses, trees and other living
things that are true plants. (Most bacterial cells also have walls, but that's another topic.)
It wasn’t until the 1960s that fungi were placed in their
own kingdom. Ecologist Robert Whittaker thought they should be separated from
plants because they are decomposers, not producers. In other words, they break
down and absorb organic matter, whereas plants make organic matter by
photosynthesis. In ecologists’ terms, fungi are saprotrophic (literally, rot feeders)
whereas plants are autotrophic (self-feeders). There are exceptions in each group, but they’re in the minority.
Other differences became apparent as the decades went by. Fungal
cell walls, for example, are made of chitin, long chains of modified glucose
molecules. That’s the same material that forms the exoskeletons of insects. Plant cells, however, are mostly cellulose, twisted and bundled chains of glucose
without the modifications present in chitin.
Other differences appear inside their cells. Fungal cells
have no chloroplasts, the organelles where photosynthesis takes place. They
also lack chlorophyll, the green pigment primarily responsible for absorbing
light energy. That makes sense, since fungi aren’t photosynthetic.
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| Plant cells (left, from a moss) contain chloroplasts, the green organelles where photosynthesis takes place. Fungal cells (right, from a Morchella, or morel, mushroom) do not. This is one difference between plants and fungi. Moss cells: Kelvinsong, CC BY 3.0, via Wikimedia Commons. Morchella cells cropped from image by Marc Perkins CC BY-NC 2.0, via Flickr. |
There are other differences, but maybe these are enough to show that fungi and plants aren’t closely related. Even so, the line between them can be muddy. Some older botany textbooks include at least a chapter about fungi. And as mentioned above, mushrooms and other large reproductive bodies are still called “fruiting” bodies, even though they’re not at all like the fruits produced by flowering plants.
It can be confusing. What’s not confusing or unclear is
that fungi, though not plants, are important to plants for many reasons. For
example, fungi made it possible for plants to colonize land, a step in development
not only for plants but for entire terrestrial ecosystems. More on that in the
next post.
