Including:
Tanacetum bipinnatum
Tanacetum camphoratum
Tanacetum corymbosum
Tanacetum douglasi
Tanacetum horonense
Tanacetum parthenium
Tanacetum pathenium
Tanacetum vulgare

Tansy can refer to any species of the genus Tanacetum (Asteraceae), but more usually means Tanacetum vulgare, sometimes called common tansy or garden tansy, while the other Tanacetum species always have some modifier in the name.

The name tansy is also sometimes given, improperly, (e.g. in the western United States) to ragwort, because in those areas ragwort is known as "tansy ragwort".

The plant was introduced into North America from Europe and has now escaped from cultivation, occurring as a weed along waysides and fences from New England to Minnesota and southward to North Carolina and Missouri.

Tansy is a strong-scented herb with finely divided, fernlike leaves and yellow, buttonlike flowers. It has a stout, somewhat reddish, erect stem, usually smooth, 1 1/2 to 3 feet high, and branching near the top. The entire leaf is about 6 inches long and is divided almost to the center into about seven pairs of segments or lobes which are again divided into smaller lobes having saw-toothed edges, thus giving the leaf a somewhat fernlike appearance. The roundish, flat-topped, buttonlike, yellow flower heads are produced in terminal clusters from about July to September. The plant contains a volatile oil which is poisonous.

Tansy was formerly used as a flavoring for puddings and omelets, but that is almost unknown now. But they were certainly relished in days gone by, for Gerarde speaks of them as "pleasant in taste," and he recommends tansy sweetmeats as "an especial thing against the gout, if every day for a certain space a reasonable quantitie thereof be eaten fasting." It has also been used as a medicinal herb. At one time it was planted next to kitchen doors to keep the ants out. Tansy beetles live almost exclusively on tansy plants growing alongside riverbanks in York, England.

One of the most curious uses of the plant in olden times, perhaps, was that of rubbing it on joints of meat to prevent the attacks of flies; but how the flavour that was thereby imparted to the meat was got rid of we do not know. Perhaps, as the plant was commonly used in cookery, a tansy-flavoured joint of meat was always welcome, as in some parts of Europe it is customary to insert a clove of garlic in the top end of a leg of mutton, that in the process of cooking the entire joint may acquire the flavour of the vegetable that it is almost a sin to think of in polite society.

An old poem on the delight of tansy is as follows:

And where the marjoram once, and sage, and rue,
And balm, and mint, with curl'd-leaf parsley grew,
And double marigolds, and silver thyme,
And pumpkins 'neath the window climb;
And where I often, when a child, for hours
Tried through the pales to get the tempting flowers,
As lady's laces, everlasting peas,
True-love-lies-bleeding, with the hearts-at-ease,
And golden rods, and tansy running high,
That o'er the pale-tops smiled on passers-by.