Jared Diamond spends a lot of time in GGS making excuses for groups that didn’t do much domestication of animals and plants. Sometimes the excuses are valid: farming was hard for Eskimos. Mostly they’re not: the wild ancestors of horses and cattle (tarpans and aurochs) were dangerous and mean, not obviously tameable. Yet they were domesticated. His arguments are even worse for domestication of plants. There are many plants that could be domesticated ( yes, there are lots of plants in Africa) – the problem is that once you have a working domesticate, wild but potentially domesticable plants have to complete with that finished, optimized product. “In order for anybody to want to plant a new crop it’s going to have to make them money, to do as well or better than crops they have now,” That and you have to have locals that want to do this. Before the Bantu, the hunter-gatherers of southern Africa never showed much interest in settling down.
So the good is the enemy of the new.
One important factor that has suppressed many locally-developed plants (likely including goosefoot & sumpweed, domesticated in eastern North America) is what you might call ‘alien advantage’. If you grow a crop near its origin, there will be local pests and pathogens that are adapted to it. It you try growing it in a distant land with a compatible climate, it often does very much better than in its own country. So… crops from Central and South America have done very well in Africa, or sometimes in Southeast Asia. Rubber tree plantations work fine in Malaysia and Liberia but fail in Brazil. Maize is the biggest crop in Africa, while manioc and peanuts are important. Most cocoa is grown in Africa: most coffee is grown in South America. Except for civet coffee of course, out of Vietnam. The perfect gift.
If you are thinking about a new domestication, you should keep alien advantage in mind. You might want to raise a domesticated prickly pear in Australia. Or maybe not…