Dear Straight Dope:
I checked your archive and I couldn't find anything about this, so I thought I'd ask you. Years ago I remember reading that scientists were extremely vexed about the evolutionary appearance of Venus flytraps. The article I read said that the little evil-looking plants simply appeared some time in our planet's history without any apparent relatives, and the creepiest thing is that their (very small) native area is right in the middle of where a meteor hit the earth years ago. Is this true? It sounds very "Little Shop of Horrors" to me. Additionally, how do the plants "know" when an insect is in their maws? I didn't think plants had nerves. I patiently await your reply.
SDStaff Doug replies:
There are no scientists puzzled about the Venus flytrap, only “scientists.” The VFT is the only member of its genus, Dionaea, but it has several relatives in the genus Drosera, which also happen to be carnivorous plants, known as “sundews.” Together, these two genera make up the plant family Droseraceae. Sundews occur all over the world, while the VFT is limited to bogs throughout North and South Carolina — and, despite any X-Files episodes to the contrary, neither of the Carolinas used to be a meteor crater.
As for their closing mechanism, it’s quite well-documented and straightforward, involving very small-scale localized electrical current, triggered by the touching of special hairs on the leaf, and the selective swelling of certain cells. You can find out more on various websites such as here.
Similar rapid leaf movements occur in sundews and various other plants, such as Mimosa (“sensitive plant”).
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