Vitamin C or L-Ascorbic acid is an essential chemical required by the body for many key chemical reactions. A shortage of Vitamin C leads to Scurvy which can be fatal in severe cases.
Vitamin C is a water soluble vitamin and it is essential to take the required doses everyday as the body cannot store amounts required over a prolonged duration of time.
Though the juice of citrus fruits is a common source of the vitamin, they do not contain the highest doses of the vitamin. Orange for example has 50 mg/100 g and lemon has 40 mg/100 g.
The juices of fruits like the Kakadu Plum and Camu Camu have approximately 3000 mg/100 g.
Though there does not seem to be any requirement to search for these exotic sources of the vitamin. The recommended daily allowance in the USA is 90 mg of vitamin C, which can be comfortably satisfied by 200 g of oranges.