What is a Lemon Tree?
The lemon (Citrus limon) is a species of small evergreen trees in the flowering plant family Rutaceae, native to Asia, primarily Northeast India (Assam), Northern Myanmar or China.

It was introduced into Spain and North Africa sometime between the years 1000 and 1200 ce. It was further distributed through Europe by the Crusaders, who found it growing in Palestine. In 1494 the fruit was being cultivated in the Azores and shipped largely to England. The lemon was thought by 18th-century Swedish botanist Carolus Linnaeus to be a variety of citron (Citrus medica), though it is now known to be a separate hybrid species.

The lemon forms an evergreen spreading bush or small tree, 3–6 meters high if not pruned. Its young oval leaves have a decidedly reddish tint; later they turn green. In some varieties the young branches of the lemon are angular; some have sharp thorns at the axils of the leaves. The flowers have a sweet odour and are solitary or borne in small clusters in the axils of the leaves. Reddish-tinted in the bud, the petals are usually white above and reddish purple below. The fruit is oval with a broad, low, apical nipple and forms 8 to 10 segments. The outer rind, or peel, yellow when ripe and rather thick in some varieties, is prominently dotted with oil glands. The white spongy inner part of the peel, called the mesocarp or albedo, is nearly tasteless and is the chief source of commercial grades of pectin. The seeds are small, ovoid, and pointed; occasionally fruits are seedless. The pulp is decidedly acidic.
That is wild! This means the crusades lead to the invention of lemonade!
Although the crusades distributed the lemon through Europe, the lemonade may have originated in medieval Egypt, where a sweet drink called 'qatarmizat', containing lemons and sugar, was being sold and consumed as early as the 13th century.