Monarch milkweed plants

Ordinary milkweed grows wild on roadsides and in fields in Pennsylvania. There is an ornamental variety commonly called "butterfly weed". Here is a link to an article describing 12 species of milkweed that attract monarchs. Sightings of monarchs in eastern Pennsylvania have been rare in recent years. Here is a link to an article by Penn State explaining the reasons for the decline in Monarchs in our state.