Well, so we thought. It turns out that what I thought was ginger for the yuzu-ginger marmalade I was dreaming up was something more potato-like. The distinctive ginger smell was lacking, and when I nibbled on them they were firm and sweetly bland. (Luckily for the marmalade I still had some ginger from a local vegetable stand.) These went back in the drawer for further investigation.
Late last week a friend we'd visited on our first trip to Hokkaido came over for dinner. We shared a typical house meal - salad, miso, and rice - with an assortment of pickled things scattered about the table for variety. The miso contained shitake mushrooms, potatoes, carrots, lots of ginger, komatsuna, and these little potato-like things. They turned rather soft in the miso and had no particular flavor.
Our friend's mother happened to call while he was still here, and so we quickly sent her a photo of the mystery vegetable hoping for identification. Her immediate response was yacon. Even though I'm only a recent grower I was a bit skeptical. The yacon I know are big fatties sweetly flavored with an apple-like texture. These met neither of these criteria. A quick Facebook chat with Rhizowen Radix suggested they might be the yacon stem tubers used for propagation, but further discussion brought up the idea that they might be Jerusalem Artichokes.
I suspect, in hindsight, that they are Jerusalem Artichokes. The flavor, texture (as well as the reminders later of one of their nicknames - 'fartichokes') and appearance (along with this article) have me convinced. Rhiz's suggestion that I plant them and see what I get is also very appealing, and would give a definitive answer, of course. I could perhaps get a second shot at growing a very beautiful edible, and solve this late year mystery in a tasty way. (I still dream of using them as a green curtain alternative.)