You should make it a habit to explore every corner of Fields of Mistria at the start of a new season. Forageable items will change each month, and with this, you'll be able to complete more side quests. Rose Hip is a type of forageable flower that only appears in winter. Not only will you need the Rose Hip for the Museum, you'll also need it to complete a request from Valen. Rose Hips are a bit odd, as they only spawn in one area in Mistria, and it's not an area you're likely to consider.