Senecio congestus, also known by its common names swamp ragwort, northern swamp groundsel, marsh fleabane, marsh fleawort, clustered marsh ragwort and mastodon flower, a herbaceous member of the Asteraceae family and the Senecio genus, can be seen most easily when its bright yellow umbel flowers appear from May to early July standing 3 to 4 feet (0.9 to 1.2 m) along marshes, stream banks and slough areas where it likes to grow.