The citron (Citrus medica) is a large fragrant citrus fruit with a thick rind. 
The shape and texture is highly variable and can be oval, round, oblong, smooth and rough.  The peel is candied and  is usually used in the food industry primarily for sweets and desserts.  
The plants thrive beautifully here in Perth and if it ripens the fruits are colored yellow and emits a very aromatic scent.