As a field ecologist, it is all remembered through repetition and need. Working in Botswana, I had to learn the names of about a dozen shrubs/tress as well as about a dozen mammals. I took good notes the first day, kept looking things up the first week, then just remembered them because I had repeated it all several times a day. Now that I haven't used that information for a few years it is all forgotten and I would have to go back to my notes to remember. Same with doing vegetation surveys in Norway. The first couple of days I had to look up things in my notes, but after a couple of days of repeating the same species I'd have them all memorized. Only the rare ones, I'd have to look up again on occasion. The list of species was around 30 plants. Each summer, I'd have to refresh my memory the first few days and now that I haven't been in the field for a while I can only remember the most common ones. And I would usually only remember either the latin name, or the common name and then have to look up the other.