The speaker is mistaken, milkweeds are not native in China. They are necessary host plants for monarch butterflies. Non-native “butterfly bushes” (from Asia I believe) attract pollinators but only for nectar, caterpillars cannot eat them. Many insect and bird species are specialists, greatly preferring or solely depending on a certain native species, and planting native plants can help reverse the current huge loss of insects and birds, and we can have the pleasure of observing them up close.
