Where does starch, the source of all beers, come from?
The list of plants that over the millennia have provided starch for brewing beer is a long one. The starch produced by a plant is stored in the form of granules: several thousand starch macromolecules intertwined and enclosed in the envelope of a single granule. And several million granules in the seeds, roots, vegetative tissue of plants, or the pith of trees.
The plants store these starch granules in their vegetative organs (roots, stems, trunk) or reproductive organs (seeds, tubers, dried fruit). As a result, this starch is present in certain parts of plants all year round or at certain phases in their reproductive or growth cycles.
To brew beer, man has explored and exploited all possible sources of starch offered by the plant world, without exception. He even found a way to treat certain toxic bitter cassava tubers to make them suitable for brewing.
Parmi ces sources d'amidon, les plus connues sont les graines des céréales, cultivées depuis 10.000 ans.
Then come the tubers with the highest yield. A cassava tuber weighting 1 to 2 kg is a starch concentrate.
The leguminous plants (beans, peas, broad beans, etc.) have an interesting starch yield. Dried fruits fall into this category.
Finally, various sources of starch play an important role in the brewing of traditional beers in the countries where they are grown. Some are still used, others have fallen (temporarily!) into oblivion.
This list is not and cannot be exhaustive. It will be supplemented in the course of further research and contributions.
Gramineae : barley, wheat, maize, rice, millet (proso, sorghum, pearl, foxtail, etc.), rye, oat, fonio (Digitaria), tef (Eragrostis tef), finger/coracan millet
Chenopodeae : quinoa (Andes)
Poaceae and other grains : Bromus mango (Chile), Arundinaria japonica (Japan)
Tubercules : cassava, ignam, taro, sweet potatoe, potato, Pachypodium (Austral Africa
Tubers : piper methysticum (kava), ginger (Madagascar)
Akenes : chestnut, carob and carob-like (Argentine), gland
Starchy fruits : plantain banana (eastern Africa)
Legumes : beans, pulses (India, Bengal, Southeastern Asia)
Pith of trees : sago or palm-tree sago (Metroxylon sago)(Philippines)
 The census of all these sources of starch is an important groundwork, but one that is fraught with pitfalls. We should verify them in ancient documents or testimonies, with vernaculars names given in prolific languages.