Within minutes there was a positive identification, along with some fascinating if useless facts about these plants. They are poisonous to horses but allegedly have numerous medicinal uses. In Japan, I discovered, people go looking for them in springtime with a view to eating the tender new shoots - something like asparagus I guess. Noriko Honda-Powell's comments deserve to be shared (but try this entirely at your own risk, I cannot vouch for the fact they really are edible):
"You have to choose the right size ones, the one should be longer and fatter than a cigarette. After picking them, get rid of the skirts as they are old leaves and they are tough and unpleasant to eat. Your fingernails get very messy and this puts lots of people off nowadays.... You rip a bit of the skirt vertically while you hold the root of the skirt with the other thumb and the skirt should peel nicely around the stem. Take all the skirts off but keep the tops. Wash very well and get rid of all the soil and dirt. Branch them in the boiling water. The water will turn green because the colour runs from the top bits. Better not to boil them more than 5 minutes. When the stems turn light brown, they are ready to be used as ingredients like other vegetables. I think they are nicer when you can see a bit of whitish colour left though they are kind of brown. Popular dishes in Japan with this is chawanmushi, tamagotoji and pilau. But I personally prefers and recommend tenpura. If you use it for tenpura (tempura), make sure you get rid of water well before you mix them with butter. You chuck all the prepared ones in a butter and drop the in the hot oil. They can be quite bitter but that's what we like for early spring forage. You can make the sauce with soy sauce, dashi, and mirin. I didn't know they grow here and this post made me feel very nostalgic! Oh, if you find them too bitter, you can get rid of the top! Good luck!"
