Lemons are believed to have originated in Southeast Asia, and spread to Spain and North Africa during the Middle Ages. The cultivated variety is thought to be a hybrid of wild species of lime and citron. Lemon trees bloom throughout the year, and fruit is picked 6 or more times a year, with an average commercial tree yielding about 1,500 lemons per year.
Third century Romans believed that the lemon was an antidote for all poisons.
Lemonade was a favorite of the Chinese Emperors. Lemons made their way to the United States with the help of Catholic Missionaries and were planted in Arizona and California.
There are two different types of lemons — acid and sweet. The most common acid varieties include Eurekas and Lisbons. The acidic type is grown commercially and the sweet types are grown mainly by home gardeners. The trees bloom continuously all year and can produce up to 500 or 600 lemons a year.
CDC.gov - 5 a Day
Lemons contain 30 to 45 percent juice depending on variety, climate, maturity when harvested, and storage conditions. The extracted juice contains between 4.5 and 8.5% organic acids (mostly citric).