Some of you have no doubt noticed some large patches of yellow flowering plants around the margins of some cattail sloughs and similar wet habitats this summer. That is swamp ragwort, also known as marsh ragwort, northern swamp groundsel, marsh fleabane, or, get this, mastodon flower. It is a member of the aster family and is known to botanists as Senecio congestus , and more recently Tephroseris palustris .