As there is a classification for every thing that exists on earth, we also classify plants on various basis, and the fruits that are beared by the plants that belong to the family citraceae are so called as citrous plants and also they contain enormous quantities of citric acid.

Area of citrus? Pls. clarify the question? Did you want to mean the area where citrous fruits are grown?

Walter T. Swingle has written:

'The principal diseases of citrous fruits in Florida' -- subject(s): Citrus, Diseases and pests, Botany

Calamansi is a citrous fruit and rust stain can be removed by citric acid. Just put calamansi on affected area and let it stay for 40 minutes then gently brush it to remove the stain.

actually watermelon does contain pottasium but friuits like apples,strawberries,plums and nectarines donot contain pottasium.