Go to the scenery menu's plant displays, and click on a tree or shrub you're curious about. A window should open that gives the price, biome, and geographic origin of the plant. You should also see the same window appear if you click on one of the plants in the zookeeper's recommendation list, so you can quickly check the plants a given animal's recommendations allow, to see which ones are from the right continent.
The savannah, alpine, desert, or boreal forest animals like all the plants from their recommendation lists, as those biomes consist (so far) of just one continent and/or just one animal. For other habitats, you have to pick and choose; for instance, one tree and one shrub from the Scrub is for gemsboks, while the other tree and shrub are for kangaroos.