Botany vs. Zombies Part One: Sunflowers


I come to praise the makers of Plants vs. Zombies, not to bury them under well-tilled soil turned with manure and dusted with nasturtium seeds: they got the science right. Given that the game’s main antagonists are completely imaginary, the designers at PopCap leveraged botany surprisingly accurately to create their award-nominated game.

Plants vs. Zombies premiered in 2009, twisting the tower defense mechanic so the player sows defensive plants which repel zombies through a variety of means, including projectile peas, exploding potato mines, and catapulted frozen watermelons. Each of these plants begins with the output of a sunflower, which is where the video game botany mimics real-life.

But why is botany such a good adversary for zombies? Plants are self-sufficient in a way most other Earth beings aren’t. Most life on Earth is a product of plants’ autotrophic ability to turn photons from the Sun into physical matter. We call that process photosynthesis: It begins with a solar photon impacting the chlorophyll in a plant leaf and ends with hydrocarbon molecules, like sucrose, that you can put in your mouth. Plants are the base of the food chain, not the bottom: nothing else eats without plants. Zombies may want your brains, but they’re not going to miss the chance to snack on solar energy (in the form of cellulose and petals) on their way through your yard (or so says Plants vs. Zombies’ game logic, anyway).

While plants are not the source of photons in the real world — as Plants vs. Zombies seems to insist with sunflowers sprouting the small suns used to buy new plants — the sunflower does produce matter that humans, animals, and zombies can consume and convert into energy. And it’s true in both the game and real life that not much happens without plants turning sunlight into matter. (I can hear you already objecting: but the mushrooms! By the pool! In the fog! We’ll be talking about that in Botany vs. Zombies Part Two for fungi versus plants.)

Sunflowers are native to North and South America and are known for their phytoremediation skills, helping to remove toxins from soil. A single sunflower is actually a ton of small flowers on one flower head; the outer flowers become the infamous petals resembling a lion’s mane while the inner flowers mature to seeds. Botanists call this collection of many flowers an inflorescence, a word that glows like the flowers do.

Now, time to get your math geek on. The small flowers in the inflorescence make two intersecting spirals, one clockwise, one counter-clockwise. Both are examples of Fermat’s spiral, with each flower oriented to its neighbour at 137.5 degrees, also called the golden angle. This is the most efficient means of cramming flowers into a sunflower head. The Plants vs. Zombies team obviously had to leave this out of their game because rendering this would be expensive, but it’s cool nonetheless.

Sunflowers have better math and autotrophic powers than zombies, which might explain why Plants vs. Zombies dispenses with the daylight scenes quickly and forces you into your backyard, late at night, with nothing but a handful of mushrooms. In part two, I’ll talk about fungi, their relationship to plants, and why zombies should fear them nearly as much as the sunflower.


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