Thistledown is built to leave. Burdock is built to hitch a ride.

They’re close relatives. Burdock (Arctium) sits in the same tribe of the daisy family as the thistles, and its flower heads look like thistle heads in a bad mood: purple tufts inside a ball of green scales. The difference shows up after flowering. A thistle sends its seed up on a parachute and lets the wind decide. Burdock keeps the seed in a ball of scales, each with a tiny hook at the tip, and waits for something with fur or a coat to walk past.

A walk in the Alps

In 1941 a Swiss engineer named George de Mestral came back from a hunting trip in the Alps with burrs stuck to his trousers and to his dog. The usual telling is that he was annoyed, then curious, and put one under a microscope. He saw what you’d see: hundreds of small hooks, each catching a loop of thread.

Noticing is the short part. He filed a Swiss patent in 1951, and the US patent was granted in 1955 (No. 2,717,437). The sources I found disagree on when the Swiss one was granted, so I’d rather not say. In between, the hard part was making the hooks on purpose. Burdock grows them for free. A loom has to weave loops of nylon, cut some of them open so they become hooks, and get the hooks to stay stiff. He worked with a weaver in Lyon, and the account I found says he discovered that nylon woven and then treated under infrared light made tougher hooks. Roughly a decade went by between the walk and something that worked. The name is a squashed velours crochet: velvet hook.

What was copied

What de Mestral took from the burr wasn’t its shape. It was its arrangement: a lot of small, weak grips, none of which needs to hold anything by itself. One hook is nothing. Two hundred are a fastening you can undo by pulling, again and again.

That makes it the reverse of the thistle’s trick, which is one very light thing carried by air. It’s a good reminder that these two plants are answering the same question, how does a seed get somewhere else, with opposite bets. One gives up all its weight and trusts the weather. The other adds a grip and trusts the animals.

I keep a site full of the first kind. I’ll admit the second is the one that ended up on everyone’s jackets.