The wild greens you need to find the location of for the porridge in the Gloom-Borne Illness side quest in Zelda Tears of the Kingdom are actually Sundelions. These plants are a general cure for gloom, and can be used in a number of different recipes. For example, Sunny Steamed Mushrooms require three Skyshrooms and two Sundelions, Sunny Steamed Meat requires three Raw Prime Meat and 2 Sundelions, Sunny Fried Wild Greens is just three Sundelions, and so on. In fact, you might have run into a bunch of them on the Sky islands and archipelagos you’ve visited. That’s is where these flowers mostly grow, so be sure to stock up whenever you’re up there. Here are two locations just as an example; there are many more. The porridge also requires milk and Hylian rice, so check out this guide to see how to get those.