This sort of ties into something I'm curious about. In KGT, p. 88, {naH} was originally defined as a culinary term, rather than a botanical one:

Any part of any plant that is eaten may be termed {naH}, usually translated "fruit" or "vegetable."

But when talking about Terran food plants, it's not used for things like potatoes. Potatoes aren't {patat naH}, they're referred to with a more specific term, {'oQqar}, focusing on which part of the plant a potato is. {naH} is only used to refer to Terran plant parts that are fruits in the botanical sense: that is, "the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering." (Wikipedia) E.g., {ghIrep naH} refers to the fruit of the grape plant itself, not to other parts of the grape plant that are eaten, like the leaves. So it seems that {naH}, aside from having a broader culinary meaning of "any part of any plant that is eaten", also has a more specific usage for botanical fruits.