Ageratum houstonianum, Photo: Michael Lahanas
Ageratum houstonianum Mill.
* USDA, NRCS. 2006. The PLANTS Database, 6 March 2006 (http://plants.usda.gov).
Data compiled from various sources by Mark W. Skinner. National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
* Gard. dict. ed. 8: Ageratum no. 2. 1768
Ageratum houstonianum (Flossflower, Bluemink; syn. Ageratum mexicanum Hort.) is a cool-season annual plant often grown as a bedding plant in gardens. Herb 0.3-1 m high, leaves ovate to triangular 2-7 cm long, and 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.
Native to Central America and adjacent parts of Mexico, but has become an invasive weed in other areas.
Ageratum has evolved an ingenious method of protecting itself from insects; it produces a precocene compound which interferes with the normal function of the corpus allatum, the organ responsible for secreting juvenile hormone. This chemical triggers the next molting cycle to prematurely develop adult structures, and can render most insects sterile if ingested in large enough quantities.
Ageratum houstonianum is toxic to grazing animals, causing liver lesions. It contains pyrrolizidine alkaloids.
A. houstonianum is prone to becoming a rampant environmental weed when grown outside of its natural range. It has become an invasive weed in the eastern USA, Australia, Europe, Africa, China, Japan and New Zealand.
1. ^ New South Wales Flora Online, Ageratum houstonianum 
* Bailey, L. H. (2005). Manual of Gardening (Second Edition).. Project Gutenberg Literary Archive Foundation.
Source: Wikispecies: All text is available under the terms of the GNU Free Documentation License