Common tansy (Tanacetum vulgare) is a member of the sunflower family, found along roadsides and rivers throughout Alberta. A perennial, it has branched, erect stems (often purplish-red). It grows to 1.5 metres. Many small, yellow-orange button-like flower heads with flat tops grow in dense clusters atop the stems. The leaves resemble those of yarrow. It can be toxic to cattle, horses and humans. The leaves have a strong odor when crushed.
Common tansy has medicinal and horticultural uses, and so it may still be available in plant nurseries and from herbal remedy suppliers. It is a noxious weed in Alberta, however, and gardeners should not purchase or grow it. Remove it when it is found in your garden. Do not share plants or seeds with other gardeners.
Make every effort to control this plant in your garden. Mowing and hand pulling help to control it, but it spreads by both seed and rhizome and can re-grow from severed roots. For complete eradication, chemicals may be needed.
More on this and other weeds from the Alberta Native Species Council.