The Rutaceae is a family, commonly known as the citrus family, of flowering plants, usually placed in the order 'Sapindales'.

Lemons are small trees or spreading bushes of the rue family ('Rutaceae') and their edible fruit. The distinctive astringent flavour of the fruit, either fresh or preserved, is also used to enhance many poultry, fish, and vegetable dishes worldwide. Citric acid may amount to 5 percent or more by weight of the lemon juice, which is also rich in vitamin C and contains smaller amounts of the B vitamins, particularly thiamin, riboflavin, and niacin.

Species of the family generally have flowers that divide into four or five parts, usually with strong scents. They range in form and size from herbs to shrubs and large trees.

The family is of great economic importance in warm temperate and subtropical climates for its numerous edible fruits of the genus Citrus, such as the orange, lemon, calamansi, lime, kumquat, mandarin and grapefruit.

Most species are trees or shrubs, a few are herbs, frequently aromatic with glands on the leaves, sometimes with thorns.

More Info: en.wikipedia.org