We’ve seen that the designers of Plants vs. Zombies did a decent job with sun-lit botany, but after twilight, they seem to misplace their cheat sheets.
The main inaccuracy the game conveys is that mushrooms — the reproductive fruit of fungi — are plants. They aren’t. Fungi live in their own biological kingdom. One of the characteristics biologists use to differentiate fungi from plants is the composition of their cell walls. Plants have cellulose in their cell wall, helping to keep the cell’s innards inside and the rest of the world out. Fungi cells contain chitin, better known as the exoskeleton of insects and crustaceans, and the beaks of squids. Genetic studies show fungi are more closely related to animals than plants, which may explain why the zombies don’t seem to mind chomping on them.
Also, fungi aren’t autotrophs, as plants are, so they don’t need sunlight to grow, although Plants vs. Zombies gives you that impression, using the same mechanism of collecting suns to buy mushrooms. Instead, fungi steal carbon from other organisms — plants and animals — for energy. Some fungi do bioluminesce, creating a small amount of light through a chemical reaction within their cells. The game designers did that right: the red and yellow “sun-shrooms” in the game yield smaller amounts of sunlight than the sunflowers. Unlike the zombies, though, you shouldn’t eat bioluminescent mushrooms, as most are toxic to humans.
However, there are some good reasons for PopCap to have chosen fungi as zombie adversaries, even if they aren’t plants. Most fungi grow by spreading hyphae, thread-like structures that branch out continuously searching for food. (A bit like the zombies themselves). A network of hyphae, called a mycelium, can puncture other living organisms to steal their nutrients, such as plants and nematode eggs. Fungi can exert a pressure as strong as 1200 pounds per square inch, even though individual hyphae may be only a few centimeters long. This indiscriminate procurement of food, so similar to the zombie, is yet another reason fungi make a formidable opponent.
Although accurate botanical knowledge gives you little advantage against the zombies in Plants vs. Zombies, I hope you’ve enjoyed seeing what real science lies under the enemies of the game’s gray and groaning pixels.