Tanacetum sp. flower. This perennial plant, commonly known as the tansy, is a member of the daisy family (Asteraceae, formerly Compositae). Tansys flower in June and July. They are medicinal plants, used to treat, among other things, tooth ache, insect bites, asthma and arthritis. They are also used as an insect repellent. The centre of the flower (yellow) is actually a cluster of tiny individual fertile flowers, or florets. The showy outer red petals are sterile ray florets.