Yep,
Equisetum. Only dinosaurs can eat it, because it is so high in silicon, so it has been laughing ever since they went extinct. Strikes terror into the heart of most conventional gardeners, but I'm sure us permies are made of tougher stuff! Supposedly you can scour pots with it. Wouldn't want to try and
compost it, but I'm sure properly toasted it would be a good supply of minerals back into the soil.