What Do Basil Plants Think About?

I’m just going to get even nerdier on the subject of essential oils and flavor this week, so those of you who’d rather I did something else — like actually make some lemon curd or something — better bug out now.

Writing about plant toxins yesterday got me thinking, notably about alkaloids (the bitter compounds that give leafy greens their character) vis-a-vis essential oils. And I began to wonder: might there be anyone out there asking why toxic alkaloids aren’t at all smelly, while (also toxic) essential oils are some of the most odiferous chemicals found in nature? Of course the answer is almost certainly no. Still, I think it’s an interesting question.

The reason essential oils are smelly (volatile) is to advertise their presence to predators. If you’ve ever brushed up against a basil bush in the garden you know exactly what I mean. Just a little agitation is all it takes to release a wave of pungent basil aroma. It’s the plant’s way of shouting out (mostly to bugs) “I’m toxic! Don’t eat me!” in the same way many insects advertise their bodily poisons to birds with bright colorings. “Don’t get any big ideas, buster!” those colors say. “Eat me and you’ll be sorry!” Obviously there are plenty of other insects that opt for the opposite: a low-profile defense, which is probably the tactic that alkaloid-containing greens take, only showing their chemical fangs (such that they have) when you nibble on them.

But clearly the whole shout-it-to-the-four-winds mechanism breaks down where humans are concerned, since basil smells pretty sweet to most people. Which only makes me think that by and large basil plants are a lot more worried about insects than they are about humans swiping the odd leaf or two. Then again there are plenty of other plants and weeds out there that are indeed poisonous to larger animals like humans, and many of those give off smells when you touch them. Since basil isn’t toxic to us in any serious way, maybe it’s hoping to be mistaken for one of them — in the same way that a harmless king snake hopes to be mistaken for a deadly coral snake.

But while that ruse may work out in the bush, the game has long been up in the garden, where humans now cultivate basil and other plants for the very aromatic qualities they once relied upon for defense. But there again: why is that? Why do we prize aromatics (i.e. volatile essential oils) so highly for eating? The answer to that is even geekier. Come back for more on that later today if you wish.