The information board at the base of the plant reads "Citron - Citrus medica. Unlike the other citrus which you peel to get at the juicy bits, this huge fruit is predominantly rind and pith or 'albedo'. This is widely used in the food industry as candied peel and the market is rising in the USA for the soluble fibre found within the albedo".

Throughout human history the Citron has had a different use, that of a medicinal plant. It was used to combat seasickness, pulmonary troubles, intestinal ailments and other disorders.
Citron juice with wine was considered an effective purgative to clean the system of poison. In India, the peel is a remedy for dysentery. The distilled juice is given as a sedative. The candied peel is sold in China as a stimulant, expectorant and tonic. In West Tropical Africa, the citron is used only as a medicine, against rheumatism. In Malaya, a decoction of the fruit is taken to drive off evil spirits. In Panama, they are ground up and combined with other ingredients and given as an antidote for poison. The essential oil of the peel is regarded as an antibiotic.
(Morton, J. 1987. Fruits of Warm Climates.)