It can be a daunting task, because there are only 4 Magic Plants and almost 600 possibilities. I managed to find all 4 Magic Plants by breeding randomly the first time I played the game, but it took me 3 weeks of intensive play.

I recommend a more methodical approach (with or without spreadsheets) that will help prevent breeding the same plants over and over again. Pick one plant and breed that with every other type of plant that you have in your inventory. Breed those offspring with the original plant, and so on. Soon you'll be discovering plants you haven't seen before. And don't keep more than 2 seeds of each offspring, or you'll totally run out of room!

If you're really desperate, there is a screen shot here with 3 of the 4 magic plants pictured. One is mostly behind the fountain, but you can get a glimpse of it and probably figure it out.