People do not know for sure where lemons have come from. However, most people think that lemons first grew in India, northern Burma, and China. The lemon is the common name for "Citrus limon." A lemon is a yellow citrus fruit. It is related to the orange. Lemon juice is about 5% citric acid, and has a pH of 2 to 3. Lemon plants vary in size yet stay generally small. The tallest height they can get is about 6 meters tall.