It’s a bad translation using a more modern meaning of “erdapfel” instead of a medieval one. Could easily be a very local colloquialism instead of a widespread name.
To my eye it looks like a melon or gourd plant. It’s definitely not a tuber (the next drawing shows an underground bulb).
Topinambour would have been available in the middle ages. Confusion with potato by the modern reader is understandable, as a topinambour does look similar to a potato, and some German dialects (e.g. Swiss dialects) name potatoes "Erdapfel".
> Topinambour would have been available in the middle ages.
No, Helianthus tuberosus [1] aka "topinambur" is Jerusalem artichoke which would not have been available at the time. It's a New World crop just like the potato.
We're talking about a book written in 1462, before the Columbian exchange. The plant wasn't introduced to Europe until the early 17th century.
The reason I think it's a heirloom melon variety is threefold: a) "earth apple" fits because melons grow on the ground, b) there are green melons with yellow and pink stripes/patches, with the same elongated fruit shape, c) vines and leaf shape.
Hello, OP here. We didn’t yet have access to a proper critical commentary and did our best with the image captions, although our best was a rather poor job in this case — much trickier than anticipated. I went to the Berlin Staatsbibliothek today for research and new captions will go live tomorrow. (Although even the experts are confused as to what the “Jerusalem artichoke” image is supposed to be — they suggest watermelon or cucumber.)
Wiktionary says of Erdapfel (which OP admittedly with '?' wasn't sure how to translate):
> From Middle High German ertapfel, erdapfel, ertöpfel, erdöpfel, ertaphel (“mandrake, cucumber, pumpkin, melon”), from Old High German erdapful, erdaphul (“pumpkin, squash, melon”)
To my eye it looks like a melon or gourd plant. It’s definitely not a tuber (the next drawing shows an underground bulb).