Is it possible that a farmer or gardener who spent decades growing a particular genus of plants will have attained a reliable intuition, or gut knowledge of the traits of the rest of the genus, and the reason for variations?
Some people can grow a species of plant for decades, and they might know that one species very well, but they might not understand anything about its close relatives in the same genus.
If, however, the person grew a number of different species within the same genus for many years, they certainly might have a pretty good idea what traits they all have in common, and what variations they all commonly tend to have.
But really it all depends on how much curiosity and interest the person has. Not everyone thinks like a taxonomist.
It is possible, yes. You don’t need a formal education to correctly identify a species. Farmers and gardeners network with one another and learn from each another. These people hold a wealth of knowledge that is extremely valuable. For example, my Dad farmed many years and though he isn’t academically inclined, he is very skilled at identifying organisms.
Traditional Ecological Knowledge (TEK) is something that I have a great deal of respect for. I think there is too much of an emphasis on formal education in order to be qualified or respected to identify something. Someone who learns something in a book or lecture is not superior to those who learned information passed down from their ancestors.
Another important detail to consider is that species often have several common names and can cause some confusion. People have had disagreements about a species ID while using different common names. Scientific names are useful for confirming species identifications especially, with widely distributed species from different regions. Lastly, you don’t have to be fluent in Latin to use scientific names.
I can think of a commercial gardener with a lot of experience growing pea varieties, vetch, beans, was able to correctly identify a problem with fabacea trees and correct it.
I was also impressed with someone who has been growing tomatoes, and was able to transfer the knowledge to start a flourishing greenhouse of various peppers.
Experience+open mind(analytical thinking), in other words.