Potatoes are not allowed in Jainism. They are considered root/underground vegetables (kand-mool). Harvesting them tends to harm many life-forms and destroys the whole plant, which goes against ahimsa (non-violence). This view is shared by both Digambar and Shwetambar traditions, though local practices can vary a bit during specific vows or fasts. In short: even if a potato were to appear above ground, the underlying principle remains the same, so Jains typically avoid eating potatoes.

You can read more on the topic here and related notes on root vegetables in Jain practice.