Readily available all year round and available in multiple types: navel, jaffa, mandarin, clementine, tangerine, blood, etc. Oranges are an excellent source of vitamin C. As well as vitamin A, the B vitamins, amino acids, beta-carotene, pectin, potassium, folic acid, calcium, iodine, phosphorus, sodium, zinc, manganese, chlorine and iron.
They do have to be peeled– which is a bit of a faff. And you should leave as much of the white pith on as possible, as it’s packed with nutrients (be careful – it can be quite bitter though). Also, halve them and then de-pip – just before adding to the blender.
You’ll find that they don’t blend completely and will give the smoothie a “chewy” texture. This is not unpleasant and is hard to get rid of – without running the blender for so long that the mixture will warm up on you. Best just to embrace it! The alternative is to use orange juice instead – which normally works fine.