http://www.crcweb.org/Passover/Quinoa%20-%20Pesach%202012.pdf

Although the vast majority of Jews in the world do not regard potatoes as kitniyos and eat them on Pesach, there are opinions which rule otherwise. The community of Padua forbade the eating of potatoes during Pesach since they regarded them as kitniyos. The author of the Chayei Odom in his additions/commentary  Nishmas Odom [hilchos Pesach responsa 20] states that  in the years 5531-2 (1771-2) there was a famine in Germany  and the Beth Din permitted the eating of potatoes, because in Germany they did not eat them on Pesach since flour was made from potatoes. The Pri Megadim, [Mishbetzos Zahav  Orach Chaim 453:1] who lived in Berlin, also mentions the opinion that potatoes are kitniyos, but in a more indirect manner.