Luffa

Luffa is a vigorous annual climbing vine with tendrils, large yellow flowers and long cylindrical fruit up to 60 centimetres. Young fruit is green and soft and cooked as a vegetable, while mature fruit dries into a tough tan network of fibres that form the loofah sponge, and in the cavities lie many flat, oval seeds, 10 to 12 millimetres long. The seeds are black or dark brown with a slightly winged margin and a smooth or finely pitted coat, and in some varieties they are white or tan. Seeds are sold in packets for gardeners, and the sponge is sold as a bath and kitchen product. The seed kernel inside is oily and has a bland to bitter flavour.

Luffa is thought to have originated in tropical Asia, probably India, with the smooth form L. aegyptiaca, though the species name suggests Egypt due to a mistake by early European botanists. It has been grown for centuries in India, China, Japan, Southeast Asia and Africa, and was introduced to the Americas by Spanish and Portuguese traders. The word luffa comes from the Arabic lufah or luf, applied to the plant, which was transcribed into European languages by Linnaeus, and loofah is a variant spelling.

Luffa has long been cultivated in tropical Asia as a vegetable and a source of fibre. Chinese writings from the Tang dynasty and later describe sigua, or silk gourd, and Japanese gardeners grew hechima, whose stem sap was used in cosmetic lotion for skin, a tradition that continues today as hechima water. In India, the young fruit, called turai, is a common summer vegetable, and seeds are sometimes pressed for oil.

The Arabic word lufah entered European botany through trade and the study of Egyptian plants, which led to the name aegyptiaca. The dried fibrous sponge became popular in Europe and North America as a bath sponge by the nineteenth century, and during the Second World War, the sponge was used in naval ship engine filters in the United States because supply from other sources was cut off.

Farmers in West Africa and Southeast Asia press the oil-rich seed for oil used in cooking and soap, though the seed contains bitter compounds that must be handled with care. Modern research has examined the seed oil as a possible biodiesel and food oil, though it remains a minor crop. Gardeners worldwide grow luffa on trellises for the sponges, and seed saving is common among enthusiasts.

Seeds are saved and planted in warm weather, since luffa needs a long hot growing season, and they are soaked before sowing to speed germination. In some regions the seeds are pressed for oil used for cooking, lamps and soap, and they have been roasted in small amounts in local diets, but only with local knowledge. Young green fruit is peeled and cooked in curries, stir-fries and soups. Mature dry fruit becomes the loofah sponge used for scrubbing the skin, dishes and filters, and for crafts and insulation. Stem sap is used in some cosmetic products.

Young luffa fruit is low in calories and provides some fibre, vitamin C and minerals. The seeds have been studied for their oil content, which is rich in unsaturated fatty acids, and for protein, but they are not a standard food, and research on their safety is limited. Traditional medicine in Asia has used seed extracts and other parts of the plant for various conditions, but there are no reliable human trials, and none of these uses can be recommended.