Ageratum

File:Ageratum houstonianum0.jpg

Bluemink (Ageratum houstonianum)

Ageratum (Template:IPAc-en) (whiteweed in the US) is a genus of 40 to 60 tropical and warm temperate flowering annuals and perennials from the family Asteraceae, tribe Eupatorieae. Most species are native to Central America and Mexico but four are native to the United States.

They form tussocks or small hills. They grow to a height of . The opposite leaves are cordate or oval, hairy or tomentose. The margins are slightly toothed or serrate. The leaves form compact clusters.

The fluffy flowers are lavender-blue, pink, lilac, or white, and spread in small compound umbels. They give small, dry fruits.

Cultivation

Ageratums are grown for their flowers, especially A. houstonianum.

Most common ageratums, "Hawaii" for example, are a short when full grown. Tall ageratum are also available in seed catalogues. They are about in height with blue flowers. There is also a medium-height snowcapped variety, white top on blue flowers. The blues are most popular and common, but colors also include violet, pink and white. Their size and color makes ageratums good candidates for rock gardens, bedding, and containers. They grow well in sun or partial shade, from early summer to first frost. They are quite easy to grow, producing a profusion of fluffy flowers all season long.

Toxicity

Several species of Ageratum are toxic, containing pyrrolizidine alkaloids. Ageratum houstonianum and Ageratum conyzoides cause liver lesions and are tumorigenic.

Weed risk

Ageratum conyzoides and Ageratum houstonianum are prone to becoming rampant environmental weeds when grown outside of their natural range.

Species

since July 2020Template:Dated maintenance category (articles), Plants of the World online has 40 accepted species:  

Selected synonyms include:

• Ageratum altissimum Template:Au – synonym of Ageratina altissima Template:Au
• Ageratum anisochroma Template:Au – synonym of Ageratina anisochroma Template:Au
• Ageratum isocarphoides Template:Au – synonym of Ageratum echioides Template:Au
• Ageratum lavenia Template:Au – synonym of Adenostemma lavenia Template:Au
• Ageratum lucidum Template:Au – synonym of Ageratum corymbosum Template:Au
• Ageratum meridanum Template:Au – synonym of Ageratum microcarpum Template:Au
• Ageratum nelsonii Template:Au – synonym of Ageratum elassocarpum Template:Au
• Ageratum oliveri Template:Au – synonym of Ageratum oerstedii Template:Au
• Ageratum panamense Template:Au – synonym of Ageratum riparium Template:Au
• Ageratum pohlii Template:Au – synonym of Teixeiranthus pohlii Template:Au
• Ageratum radicans Template:Au – synonym of Ageratum peckii Template:Au
• Ageratum salicifolium Template:Au – synonym of Ageratum corymbosum Template:Au
• Ageratum stachyofolium Template:Au – synonym of Paneroa stachyofolia Template:Au

Segregate genera

The genus Paneroa consists of one species, Paneroa stachyofolia, native to Oaxaca, which was first described in Ageratum but which seems to be more closely related to Conoclinium and Fleischmannia.