There are at least eight species of the pumpkin family in Botswana, of which the tsama melon, Citrullus lanatus, is the most distinctive and frequently seen. It is found throughout the region, and is particularly common after a good rainy season. Then, even after most of the rest of the vegetation is brown and shrivelled, you'll find tempting round melons beside the sandiest of roads – often apparently on their own.
During the dry season these become important sources of moisture for many animals, especially the gemsbok, and are also used by the local people. To get drinking water from one of these, you first cut off the top, like a boiled egg. The centre can then be cut out and eaten. Then take a stick and mash the rest of the pulp whilst it's in the melon, and this can be eaten. Take care not to eat the pips. These are best roasted and pounded, when they make an edible meal that can be cooked with water. Sometimes you'll come across a bitter fruit, which you should not eat as it may cause poisoning.
Another fairly common species is the gemsbok melon, Citrullus naudianus
, which has similar sprawling tendrils and an oval fruit, covered in blunt fleshy spines. Unlike the tsama melon, this is a perennial plant with a long underground tuber. Inside the fruit is a jelly-like, translucent green which can be eaten raw (again, discarding the pips usually), though it doesn't taste very good. It's slightly more palatable when roasted beside the fire overnight – but I wouldn't recommend that you throw away your muesli or yoghurt before tasting it!