Ageratum Explained

Ageratum [1] (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 30inches. 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 6inches-8inchesin (-in) when full grown. Tall ageratum are also available in seed catalogues. They are about 18inches in height with blue flowers.[2] 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.[3] [4] [5] [6]

Weed risk

Ageratum conyzoides and Ageratum houstonianum are prone to becoming rampant environmental weeds when grown outside of their natural range.[7] [8]

Species

, Plants of the World online has 40 accepted species: 

Selected synonyms include:

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.[9]

Notes and References

  1. Sunset Western Garden Book, 1995:606–607
  2. Web site: Ageratum price 2022 – current wholesale market global prices. Husfarm Agriculture platform. 2023-07-05. 2023-07-05. https://web.archive.org/web/20230705083121/https://husfarm.com/product/ageratum. live.
  3. Acamovic, T., Stewart, C.S., Pennycott, T.W.,"Poisonous Plants and Related Toxins", 2004
  4. Noa, M., Sanchez, L.M., Durand, R., "Ageratum houstonianum toxicosis in Zebu cattle", Veterinary and human toxicology, 2004, vol. 46, no. 4, pp. 193–195.
  5. Sani, Y., Bahri, S., "Pathological changes in liver due to the toxicity of Ageratum conyzoides", Penyakit Hewan (Indonesia), 1994, v. 26(48) pp. 64–70 http://www.fao.org/agris/search/display.do?f=./1997/v2304/ID9600846.xml;ID9600846
  6. Fu, P.P., Yang, Y.C., Xia, Q., Chou, M.C., Cui, Y.Y., Lin G., "Pyrrolizidine alkaloids-tumorigenic components in Chinese herbal medicines and dietary supplements", Journal of Food and Drug Analysis, Vol. 10, No. 4, 2002, pp. 198–211 https://www.nlfd.gov.tw/en/ch/MultiMedia_FileDownload.ashx?guid=304d1580-c6aa-4502-900e-cab744c31985
  7. Web site: Global Compendium of Weeds, Ageratum conyzoides (Asteraceae) . 2009-06-21 . 2020-02-24 . https://web.archive.org/web/20200224185757/http://www.hear.org/gcw/species/ageratum_conyzoides/ . dead .
  8. Web site: Global Compendium of Weeds, Ageratum houstonianum (Asteraceae) . 2009-06-22 . 2023-02-16 . https://web.archive.org/web/20230216143311/http://www.hear.org/gcw/species/ageratum_houstonianum/ . live .
  9. 10.3417/2007173 . Paneroa, A New Genus of Eupatorieae (Asteraceae) from Mexico . 2008 . Schilling, Edward E. . Novon: A Journal for Botanical Nomenclature . 18 . 4 . 520–523 . 85729667 . 2023-01-21 . 2023-11-08 . https://web.archive.org/web/20231108142313/https://www.biodiversitylibrary.org/part/58019 . live .

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