An indigenous crop of the Americas, tobacco is cultivated for its leaves. However, for commercial growing the flowers are cut off as to encourage the leaves to grow further down the stem. Differences in soil and climate produce leaves that have specific characteristics and require different methods of fertilization, insect and disease management, harvesting and curing. All tobacco varieties belong to the Nicotiana genus, although the main source of commercial tobacco is Nicotiana Tabacum. Nicotiana Rustica is also grown, albeit to a far lesser extent, and used in Oriental tobaccos.