Tangerines Citrus reticulata, as a genus are not represented in Africa, although there is one obscure, very Citrus like member of the citrus family present, and that is Citropsis daweana. The Mozambique 'Cherry Orange' is a small tree with citrus smelling leaves, and small, probably edible fruit that grows in riverine valleys in Mozambique and Zimbabwe. So when we radiated to Myanmar (Burma), South East Asia, and southern China, the possible origin of the mandarin, we would have been meeting wild citrus not too different from Citropsis, except a bit larger and more edible. The wild ancestral form of the mandarin hasn't been found; either that or the mandarin is ancestral to both the orange and mandarins.
Edibility is fairly widespread in the citrus as a group, with quite a few of the 35 or so species being a potential food item. But the mandarin is one of the best. As with most citrus and other good things, the rise of agricultural settlement and both land and sea trading between Europe, the greater Mediterranean through South West and South Asia to China, resulted in the spread of the mandarin into all these areas. In time, the mandarin was spread to Spanish, Portuguese, and- eventually - British colonies. The tangerine was introduced to Australia by the British colonizers in the nineteenth century, and from Australia to New Zealand shortly after.

Mandarins don't travel quite as well as oranges, but they can be cool stored to extend their availability, and the complex hybrids now being produced have better storage and handling characteristics. Hybrids include tangelos (tangerine x grapefruit), tangors (tangerine x orange), and tangtangelos (tangerine x tangelo). Mandarin hybrids, in particular, look set to become a standard market fruit, and excellent nutritional value.

Tangerines are a good source of vitamin A - in fact, they rank number 5  in the list of top sources from commercial fruit, with 920 International Units per 100 grams. They are a very good source of vitamin C - one fruit provides almost half an adults daily requirement.
Tangerines have natural plant chemicals ('phytochemicals') called 'monoterpenes' in their skin that both protect against cells becoming cancerous, and help fight existing cancers. At least, as studied in laboratory mice - but there is no reason to think these chemicals wouldn't be active in humans. Unless they are certified as 'organically grown', commercial citrus may have been dipped/sprayed with anti fungal chemicals to prevent storage rots (they may also be dyed to heighten the color, and waxed with a vegetable derived wax to heighten the appearance). Therefore it is advisable to select only organic fruit to chew on the peel. It is unknown if the tumor fighting chemicals survive heat and processing when marmalade is made.