In my Mandarin text (I'm in the penultimate chapter, #49!) we're reading about Chinese medicine. One of the readings tells of a student (Korean) who is persuaded to see a traditional doctor when she gets a stomach upset. He heels her pulse, asks her a few questions, then tells her to pick up some 山楂 shanzha, Chinese hawthorn (or haw) at the market and eat some when she has a chance. She does this, and is soon on the mend, though she wonders that the doctor prescribed no medicine. Of course - you've guessed the punchline already - shanzha is medicine (someone told me early in my stay that I must understand that in China food is medicine), and happens to be just what the doctor ordered for digestion. So that's what that entire aisle of red things at the supermaket is about, where you can shanzha in rolls, disks, sheets, etc.