Imagine you're a fragile little tomato seedling, just growing your hearty way up towards the sun without a care in the world. One day, a vine nudges its way through the soil nearby, and it looks pretty ordinary and you think how nice to have this new neighbour at your side. Yes, its grasping little tendrils are getting a little too close for comfort, but you're a level-headed tomato seedling and you don't like to panic. Besides, you can't exactly pack up and move (LOL). You just wish the vine would respect your personal space and not wrap itself quite so tightly around your stem, because you're starting to feel a little light-headed and you're pretty sure something is sucking out all your life-giving phloem with its murderous haustorium.

That (with just a sprinkling of poetic license) is a story about the leafless, parasitic Cuscuta vine, also known as dodder. Or, more aptly, the strangleweed. Or, even more aptly, the hellbind. Native to North America, it is a true parasite – a freeloader that gorges on nutrients and water from its host and produces nothing itself. 

What's really interesting is how the vine searches out its prey ... because as far as parasites go, it's a bit of an overachiever – and it won't settle for just any old host. When presented with a range of host options in experiments, the vine, in this case Cuscuta pentagona, has shown itself to be remarkably discerning, twisting its way only towards the most desirable and nutritious option. How? Thanks to a (disconcerting) ability to 'smell out' its victim. 'Smelling' in the plant sense, that is – by picking up the pheromones, or chemical signals, that plants emit. 

What's even more fascinating (or unsettling, if you're a tomato plant), is what happens after the dodder vine latches on to its host. Studies have shown that while nutrients and water are being siphoned out, there's another kind of exchange going on as well: a sort of two-way genetic shuffle, a tactic that scientists speculate might help the dodder weaken its host plant, making it easier to control (more on that here). 

In a nutshell, Cuscuta is a brilliant, calculating plant vampire. But don't just take my word for it. Watch this clip from Through the Wormhole for yourself ... if only for the joy of listening to Morgan Freeman expertly narrate a story about serial killer plants. 

H/t: Maggie Koerth-Baker. Join her 'Fellowship of Three Things' here.

Top header image: BlueRidgeKitties, Flickr