Ageratum houstonianum (Flossflower, Bluemink; syn. Ageratum mexicanum Hort.) is a cool-season annual plant often grown as a bedding plant in gardens. The flowers are usually blue (though sometimes white, pink, or purple), the heads borne in dense corymbs. The ray flowers are threadlike, leading to the common name.

It is apparently native to Central America and adjacent parts of Mexico, but has naturalized in other areas, especially coastal areas of the eastern United States and Pacific islands.

Ageratum also has an ingenious method of protecting itself from insects. This being a chemical that when eaten, effects the insects juvenile hormone rendering their larvae sterile.

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