Vampire plants are real. They don’t turn into bats or cringe in daylight, but they do suck the life from other plants.
Epiphytes like Spanish moss and orchids aren’t vampires. These harmless plants are primarily looking for structural support. Dodder, though, is a parasite looking for a free meal. It looks more like spaghetti than a plant. It’s a leafless, rootless, thread-like plant that latches onto a variety of host plants. You’re not likely to see it in your yard, but where it does grow it looks like a net of yellow-orange Silly String thrown over shrubs or herbaceous plants. It survives by taking nutrition from another plant.
When a germinating dodder seedling makes contact with a suitable host, it winds around the stem and sinks a root-like appendage, called haustoria, through the tissue to fuse with the host’s vascular system and siphon out nutrients and water. Once the connection is made, dodder no longer needs the soil. Its root system dies, and the plant will exist solely on the host plant. It will begin branching out, weaving strands over the host and nearby plants.
It’s essential for dodder to find a host. Because it minimally photosynthesizes, it only has about a week after germination before it runs out of food stored in the seed. To improve its chance of survival, dodder evolved to sniff out its prey.
All plants release volatile organic compounds, or VOCs, to attract pollinators or bolster their defenses. When an insect feeds on a plant, the plant will emit certain VOCs. When detected, nearby plants can change their leaf chemistry to repel insects or make foliage less palatable. Plants can even call for help. When aphids are present, VOCs can signal beneficials. Certain insects, such as parasitic wasps, will heed the call and swoop in to feed on the aphids.
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Dodder evolved to detect plant VOCs. Not only that, it can grow in the direction of preferred hosts. At the Trident Technical College horticulture program, we put this theory to the test. We seeded a row of dodder with tomato seedlings on one side and plastic sticks on the other. Dodder has a strong affinity for tomatoes and our results supported that. Not a single whip-like dodder seedling grew in the direction of the plastic sticks. Every one of them reached for the tomatoes.
Dodder evolved to detect volatile organic compounds, which are released by all plants to attract pollinators or signal distress. A seedling must find a host within a week after germination and will grow in the direction of its preferred host plant by following its VOCs. Tony Bertauski/Provided