At TheGenieLab we take personal development seriously. As such knowing your clemetines from your satsumas, and your tangerines from your onions, is important.
They are all varieties of mandarin.
Mandarins originated in China, and have been grown for thousands of years. They were a delicacy for the higher echelons of society. They only arrived in Europe in the 1900s.
Clementines are small with few or no seeds, and peel very easily. They are believed to be named after Father Pierre Clement who bred a hybrid orange by accident in his orphanage in Oman.
Tangerines have looser skin and are less sweet, originate from northern Africa, or at least arrived to Europe from the Moroccan port of Tangiers. Until that time, the word was used for many items that came from Tangiers.
Satsumas are from Japan, where they were originally cultivated in the Satsuma province. They also have looser skin, but retain more sweetness and again, are usually seedless. Because its loose and waxy skin, it can be difficult to know its quality just by feel and sight alone.
Nutritionally, they are all pretty similar.