Swan plants (Gomphocarpus physocarpus, milkweed) are the host plant of monarch butterflies. The name comes from the fluffy seeds (together with the ballooning seedpods and their curved stem). I found this one on Hillsborough Cemetery yesterday, fine but windy. Butterflies circling around the bushes, eggs and various sizes of caterpillars on the plants.
Wikipedia has the cryptic comment: “This plant is also popular in traditional medicine to cure various ailments.”