In message , Michael
Bell writes
It is interesting how very few species have been developed as cereal
grains. In the pre-Colombian Americas, only really maize took off,
though there is also quinoa, but only of very localised value. I think
I read in Jared Diamond's Guns, Germs and Steel that there is a N
American grass which had some use, but it has very small seeds, is
rather oily, and the flavour is something of an acquired taste. Though
teff, a small-seeded grass, is very important in Ethiopia. It is
ultimately yield rather than seed size that is the most important,
though large seeds is generally helpful. I think I read in Diamond
also, that, if Middle Eastern cereals hadn't been adaptable to northern
Europe, there is really only one local species of grass that might have
been potentially useful.

What was that one grass?

Secale cereale (rye) or Leymus arenarius (lyme grass) or ...

If you're counting pseudocereals (like quinoa) then Fagopyrum esculentum
(buckwheat).
--
Stewart Robert Hinsley