The plant most often mistaken for a thistle isn’t one. Teasel has the same look: tall, prickly, a spiny head on top of a spiny stem, standing brown and dead through the winter. But it belongs to a different family altogether, the one that also holds honeysuckle and scabious. Up close, the head isn’t a tuft of flowers with a seed-parachute each. It’s an egg-shaped cone of stiff bracts, each ending in a spine, with tiny mauve flowers opening in rings among them.

Two things about teasel have kept me reading, and they turn out to hang off the two halves of its Latin name.

The hook

The cultivated kind, fuller’s teasel, has bracts that curve over at the tip into small, strong hooks. For centuries, those dried heads were the tool for raising the nap on woollen cloth. Cloth came off the loom flat and hard. Finishers dragged teasel heads across it to pull up a soft fuzz of fibre ends, which could then be sheared level. First they did it by hand, with heads set in a wooden frame. Later it was done by machine: the gig mill, a drum studded with rows of teasels that the cloth was run against.

The obvious question is why anyone still does it this way, and some mills in Britain and elsewhere still do, for fine woollens, cashmere, and billiard cloth. Steel wire cards were invented to replace teasels, and for the rough first passes they did. Several sources say the same thing about the finishing pass, and an old account quoted in one history of the trade puts it best: when a teasel hook meets a knot it can’t get through, it breaks. A metal hook, “instead of yielding, must tear or deface the material.”

That’s the whole trick. The teasel is better because it is weaker than the cloth. A tool that fails before the work fails is worth something no stronger tool can offer. The heads wear out and have to be replaced, so the few mills that still use them have to keep a supply coming from growers. People have kept paying for that.

The cup

The wild teasel does something the cultivated one is less famous for. Its leaves grow in opposite pairs, and at each joint of the stem the two leaf bases fuse into a cup around it. The cups fill with rain and dew and can hold a surprising amount, up to around 100 ml in a big one. Insects climb in and drown. Walk past a teasel in late summer and you can find cups of brown water with bodies in them. The genus name Dipsacus is usually traced to the Greek for thirst.

In 1877 Francis Darwin, Charles’s son, looked at this and asked the obvious question: is the plant eating them? Under the microscope, he found glandular hairs lining the cups that pushed out thin, trembling threads of what he took to be living protoplasm, nearly a millimetre long, into the water. He thought they might be absorbing the dissolved remains. His father was delighted. He sent Nature a letter from Ferdinand Cohn, a leading botanist in Breslau, who had seen the threads too, and introduced it by calling Francis’s find “so new and remarkable a fact in the physiology of plants, that any confirmation of them is valuable.” Cohn compared the threads to a Pharaoh’s snake, the Victorian party trick where a small pellet, lit, swells into a long grey coil. Then, apparently, almost nobody followed it up for well over a century.

In 2011, two researchers finally ran the experiment: Peter Shaw and Kyle Shackleton, working on wild teasels in the field. They dropped dead fly larvae into the cups of some plants and left others alone. The fed plants didn’t grow any bigger, but they set about 30% more seed. They called it the first real evidence of a reproductive payoff from “carnivory” in teasel.

In 2019, James Krupa and Matthew Thomas pushed back, in a paper titled with some relish “Is the common teasel carnivorous or was Francis Darwin wrong?” Their argument, as far as I can reconstruct it from summaries (the papers themselves are behind a wall I can’t get through), goes like this. The 2011 study never measured the soil, and the larvae added a meaningful dose of nitrogen and phosphorus. That’s fertiliser, and it doesn’t matter much whether it comes in through a cup or through the ground. In their own trials, soil nutrients alone explained growth and seed set. And teasels potted in carnivorous-plant soil, the thin, nutrient-starved mix sundews are grown in, didn’t grow a stem or flower at all, however much “animal solution” went into their cups. A true carnivore should do best exactly where the soil is poorest. Their conclusion was that there was no evidence the teasel is carnivorous.

Then in 2023, a group led by Vergne went back to the threads themselves, the part everyone had stopped looking at. Using modern microscopy and staining, they found that the filaments are real and that they come out of the glands in an orderly, apparently plant-controlled way. Their title reaches back to Cohn’s image: “The Pharaoh’s snakes of the teasel.” What the threads are for is still open. They came across the threads while studying the plant’s microbiome. That makes me wonder, and this is only my guess, not their claim, whether the cup is less a stomach than a garden: a pond where the plant tends its microbes rather than digesting its guests.

So the cup question isn’t closed. The one honest summary I can give: the insects really do drown there, Darwin’s threads really do exist, and whether the plant gets anything out of either is still being argued, 150 years on.

The name

The two halves of teasel’s usefulness have ended up tangled in its Latin. Dipsacus means thirst, for the cups. The wild species is Dipsacus fullonum, “of the fullers.” But fuller’s teasel, the hooked one the cloth trade actually used, is now usually given as D. sativus, the cultivated one. Botanists still argue whether the two are really separate species at all, since they hybridise freely. The upshot is that the plant named for the fullers is the one they had least use for, and the one with the hooks carries a name that only says someone planted it.

I like that a single plant can be interesting in two unrelated ways, one as old as the wool trade and one people are still disputing. And I like that its best-known virtue is its weakness: a hook that gives way before the cloth does.