Vampire Plants

For an illustrated version, see Environmentor vol 7 no 2 pp 22-23

'Tis the season for something a little supernatural... How about a shape-shifter and a vampire?

Story: The Headley Kow

Long ago in the English village of Headley, folks were afraid of the “Headley Kow” (they pronounced it “koo”), a supernatural creature that often took the form of a fierce black horse, but could change shape to mimic animals, objects, or anything that would help it play mean tricks on the people of Headley.

They say there was an old woman who earned her living by doing laundry or mending, running errands for busy housewives, or whatever needed doing in the vilalge. She didn't earn much, sometimes just a cup of tea or a bowl of stew, but she was always cheerful saying, “Aren't I the lucky one! I have just as much as I need.”

One afternoon she was coming home from the village when she saw a big black iron pot on the side of the road. “Who could have left it there?” She looked both ways and saw nobody coming or going. “What a fine big pot, with a lid, too! But maybe it has a hole...” She came closer to examine it. “If that's why someone threw it out, though, it would be just the thing for me. I could put it by my cottage door and plant some geraniums in it. Aren't I the lucky one, to find such a fine flower pot!”

But when she lifted the lid to look for the hole, she got a big surprise. “Gracious! It's full of gold coins! What a treasure!” Her eyes grew wide as she imagined all the things she could buy. “Aren't I the lucky one! Now, how can I get this heavy thing home?”

She took off her shawl, tied it around the pot, and began tugging on the ends. And she began to worry. How could she keep such a fortune safe from robbers? Where could she hide that much gold?

She stopped to rest her back, and lifted the lid to check on the gold coins. “Gracious! Now the pot is full of silvercoins!” This put her mind at ease: silver was less valuable than gold. “Aren't I the lucky one! I won't worry so much about robbers,” and she began tugging the pot along the road again.

But the way home was long. She stopped to rest again, and peeked at her treasure. “Gracious!” for now the pot of silver coins was gone, replaced by a big lump of solid iron. “Iron instead of silver or gold! Aren't I the lucky one! Because I won't have keep this safe. I can sell it to the blacksmith, and he'll make useful things out of it–while I won't have a worry in the world!” But it was still heavy. She tied the shawl again and resumed tugging.

She had almost reached her cottage door when her back needed another rest. This time when she looked in the shawl, instead of a lump of iron she found a big stone. “Aren't I the lucky one! This just what I need to hold my door open when I want a nice breeze in the house!”

Suddenly the stone gave a shake and rose up. It dropped down four long lanky legs and a shaggy tail. It tossed long ears and a black mane and pranced away, laughing and neighing.

“Well!” said the old woman, “aren't I the luckiest one of all, to see the Headley Kow in person – after dragging it over half the countryside!” 

And she went inside to make herself a cup of tea.

 

## Science tale

Driving in the country this summer, you may have seen tangles of stringy orange stuff sprawled over roadside grasses and bushes. You may have thought, “What fool of a fisherman threw his fishline out the window? Doesn't he know it's dangerous to wildlife?” 

And that orange stuff IS dangerous, but not to wildlife. It's not fishline; it's “dodder” (a.k.a.”strangleweed” Cuscuta campestris),a vampire plant that takes its food and water from the plants it grows on.

Scientists figure that long long ago, the ancestor of dodder was a self-sufficient vine like its relatives in the morning glory family (Convulvulus). The chlorophyl in its leaves made its food using the energy of sunlight. Its roots gathered water and minerals from the soil. Its stems were weak, so it climbed up onto other plants to get its share of sunlight.

At some point, though, dodder's ancestral genes mutated. Dodder gained the ability to sink fangs (haustoria) into the flesh of the plants it was climbing on. Sucking all the food it needed from its victims, this vampire plant no longer needed chlorophyl. Without that bluegreen color, its carotenoid pigments left it bright orange. Its sprouting seeds made a tiny root just long enough for the seedling to bumble into a victim plant, but once it had sunk in its fangs, even that root dried up. It even quit making its own leaves. Now dodder is just a twining orange stem, tangling up like discarded fishline on its victim. Dodder has become a vampire parasite on other plants.

Recent study of dodder's complete genome shows that dodder has downsized like the Headly Cow, gradually losing the genes for making chlorophyl, leaves or roots. It doesn't need them to play its tricks on other plants!

Unlike most parasites, which can only attack a few victim species, dodder can grow on a wide range of dicots (including its own Convulvulus cousin, bind weed) and even some grasses! The geneticists were surprised to find genes from these species in dodder's own genome, probably gained by a process called “horizontal transfer.” They don't yet know what role these foreign genes play for dodder, but suggest they might help the vampire avoid its victims' immune defense systems. 

 

Folktale: Jacobs, JosephBatten, John D. (1894). "The Hedley Kow". More English Fairy Tales(2nd ed.). London: David Nutt. pp. 50–53 & notes: 225.

 

Facts: Footprints of parasitism in the genome of the parasitic flowering plant Cuscuta campestris https://www.nature.com/articles/s41467-018-04344-z#Fig1

SCIENCE Aug 2018 Decoding parasitic plant genomes Nat. Commun. 10.1038/s41467-018-04344-z, 10.1038/s41467-018-04721-8 (2018).