I mainly just know the cucurbits and the solanacias (sp). I need to know what I'm growing squash-wise to see if I need to save seed the hard way (intentional pollenation) or if the plants won't cross naturally. The solanacea's are good to know because of crop rotation. E.g. Don't follow this plant with a solanacia, or vice versa. I should learn how to spell it properly, though.
But I always try to learn the Names of plants, on account of the different varieties I grow. 4 kinds of raspberries, different lettuces, 10 or more kinds of tomatoes. So when I give my parents tomatoes, I point to them and say, "that's a lemon boy, etc" But my mom only caught the "lemon" part, so she asks me all the time, "When are you planting more lemon tomatoes?" Which is incorrect... plus its a hybrid and I've moved past that phase of gardening. Sigh!
Of course she still calls it "expresso" instead of eSSpresso; "Netflex" instead of NetflIx, despite constant correction. Oh well.