XVI International Botanical Congess
The farmland of Upper Egypt extends for about 1000 km between Giza (north) to Aswan (south). Weeds of this farmland comprises 248 species distinguished into: agrestal, ruderal, canal-bank plants and desert weeds which are confined to the newly reclaimed desert outskirts of the farmland. Agrestal weeds exhibit the greatest diversity and are either winter, summer or all-year plants. Winter weeds assemblages associated with ancient crops (Barley, wheat, etc.), known in cultivation since millenia of years ago, are complex in origin comprising 80-120 species each. Summer weeds assemblages associated with modern crops (Maize, cotton, etc.), introduced to Egypt 200-350 years ago are rather simple and comprise 30-40 species each of tropical species which were not known in Egypt before the introduction of these crops. Common winter weeds show apparent polymorphism when compared with common summer weeds.