In Jainism, lotus stem is generally considered acceptable, because it is not a root vegetable like potato, onion, garlic, carrot, etc.

However, it should be taken with care:

• it should be fresh and properly cleaned
• it should not involve unnecessary himsa
• it should be eaten only if it is allowed in your specific vow, observance, or tradition

So, for most household Jain diets, lotus stem can be eaten. For very strict observance, the final rule depends on the specific vrata or achar being followed.