The origins of cultivated plants have been treated rather extensively in modern times beginning with the landmark essay of Alphonse de Candolle in 1866 (2nd edition). Thinking in this century has been heavily influenced by the writings of the Russian botanist Nicolay Ivanovich Vavilov. He developed the concept of centers of origin, named them and listed a suite of plants for each one. The studies were on a global scale but, in some areas, incomplete. For example, in Africa he placed a center of origin in Ethiopia but did not investigate sub-Sahara where some important crops were domesticated. He explored the highlands of South America but did not treat the lowlands, which have a different set of cultivated plants. Nevertheless, he was a giant among investigators of the origins of plant domestications; all of us who are interested in the subject are his students.
But the origin of cultivated plants is not quite the same as the origins of agriculture although they are, of course, related. An agriculture must have a suite of plants, or plant domesticates to sustain it. The agricultures of the world do seem to have centers of origin or geographic points for their beginnings. The most studied and detailed by archaeology and history is the Near East. It was basically a wheat-barley agriculture although other crops like lentil, chickpea, pea, root crops and so on were attached to it. The wheat-barley combination was the bottom line. This agriculture spread westward around the Mediterranean, across North Africa and southern Europe and thus northward across the Balkans to western Europe, the British Isles, Scandinavia and Russia. It spread eastward to the Ethiopian Plateau and on to India. In India the wheat-barley combination found a congenial home in the highlands and was also grown in the lowlands in the winter season. This complemented rice, sorghum and millet summer crops. Wheat and barley became important in China and Japan but were not suited to South East Asia where rice was the dominant cereal.
Meanwhile an independent agriculture was evolving in Africa. There was a suite of crops domesticated in sub-Sahara with no obvious center, but the activity ranged from the Atlantic to the Indian Ocean. Plants included sorghum, pearl millet, cowpea, African rice and others. Ethiopia contributed a short list of indigenous crops, some of which are grown nowhere else. This includes tef (Eragrostis tef), noog or niger seed (Guizotia abyssinica) and ensete (Musa spp.). There are also some unique forms of Brassicas (cabbage). Ethiopia has the characteristics of a center while the sub-Sahara does not. Clearly a sub-Saharan agriculture did evolve, independently from the Near East center.
An agriculture developed in north China dating from about 8500 BP. Many of the early sites are located on the loess terraces associated with the Yellow River. The early crops were millets of one kind or another, primarily a proso (Panicum spp.) and a foxtail millet (Setaria spp.). This agriculture is noted for a wide variety of vegetables attached to it, both leaf crops and root crops. A rice agriculture developed in the lowlands, perhaps centered on the Yangzte River delta area. It was an expansive kind of agriculture and rice became important from eastern China to India and southward into Indonesia.
In the New World, a maize-based agriculture evolved in southern Mexico and adjacent areas. It was also an expansive agriculture and maize cultivation spread as far north as Canada and deep into South America. There were other crops associated, of course, but maize was the dominant cereal over a wide range of Americas. In South America an agriculture developed in the highlands based on tuber crops, among which was the potato (Solanum spp.) which became important in North America and other temperate regions. In the lowlands the dominant crop was cassava, a very important source of starch and adapted to tropical rainfall conditions.
From our review of the agricultures of the world, they seem to be centered on the Near East, Ethiopia, sub-Saharan Africa, China, Mesoamerica, highland South America and lowland South America. Each has its own suite of cultivated plants. People associated with them, their cultures and religions, are closely intertwined with the main crops they grow. This appears to be the pattern on a global scale. This view does not differ very much from the patterns described by Vavilov. A little bit has been added here and there but the overall conclusions are very similar.