Update: So here's what I've found. While using RefScope in active mode, enter the console (by pressing the ~ key) and click on the missing mesh box, then exit the console. The data window will pop up. I'm still not sure exactly what the problem is since I have a mod called ImperialCityHouse that has a few nirnroot out front, and when I click on those, it says defined in both Oblivion.esm and ImperialCityHouse.esp. However, if I go and find a different nirnroot, it just says Oblivion.esm. Also, it's looking for the meshes in a folder that doesn't exist, one called "HarvestFlora" or something. When I have more info, I'll post again for anyone who has similar problems and stumbles upon this forum.