citrus trees belong to the single genus Citrus and remain almost
entirely inter-fertile. This means that there is only one super-species
that includes grapefruits, lemons, limes, oranges, and various other
types and hybrids. The fruit of any citrus tree is considered a
hesperidium, a kind of modified berry. The large citrus fruit of today evolved originally from small, edible berries over millions of years. Recent research indicates an origin in Australia, New Caledonia and New Guinea. Southeast Asia bordered by Northeast India, Burma and the Yunnan province of China is a region in which some commercial species such as oranges, mandarins, and lemons originated. European oranges, such as Bitter Orange, were originally brought from India at around the time of Alexander the Great. Lemons reached Europe during the time of classical Rome. Florida oranges actually originated with the Spanish Conquistadors.