A single native willow tree can support over 300 different types of caterpillars. Those caterpillars feed songbirds, which feed hawks, which spread nutrients through an entire food web. That is the basic idea behind keystone native plants: some plants do far more ecological work than others. The term comes from architecture. In a stone archway, the central wedge-shaped stone—the keystone—holds the weight of the entire structure. If you remove it, the arch collapses. Keystone