This weedy annual is widespread from eastern North America to South America. Some colls. here can be referred to var. intermedia Fern., but that taxon is not recognized in recent treatments. These colls. include an unusual plant from BULL (DHL) with small broad leaves. The species often becomes abundant in recently clearly or burned woodland, probably involving germination of long-dormant seed (Baskin & Baskin 1996, Darbyshire et al. 2012) Plants have remarkably fast potential growth rate, with retention of water during dry periods, and with rapid uptake of nitrogen, including nitrogen dioxide directly from the atmosphere (Darbyshire et al. 2012). Plants appear to be somewhat unpalatable to mammalian herbivores due to pyrrolizidine alkaloids, sesquiterpenes and perhaps other compounds. However, humans have used this species for medicinal purposes (as "pilewort" etc.) and even occasional food (Fernald et al. 1958). Its chemistry is similar to that of Senecio sensu stricto (Pelser et al. 2007), and K has replaced Erechtites into Senecio.