''Ageratum'' () (whiteweed in the USA) is a genus of 40 to 60 tropical and warm temperate flowering annuals and perennials from the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Asteraceae,

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English is in the discipline of anthropology. This definition is contested, in part due to confl ...

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 30 in. The opposite leaves are cordate or oval, hairy or tomentose. The margins are slightly toothed or serrate. The leaves form compact clusters. The fluffy

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...

s 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 6-8 inches when full grown. Tall ageratum are also available in seed catalogues. They are about 18 inches 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 Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...

, containing pyrrolizidine alkaloids. ''Ageratum houstonianum'' and '' Ageratum conyzoides'' cause

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

lesions and are tumorigenic.

Weed risk

''Ageratum conyzoides'' and ''Ageratum houstonianum'' are prone to becoming rampant environmental

weed A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place", or a plant growing where it is not wanted.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. ...

s when grown outside of their natural range.

Species

, ''Plants of the World online'' has 40 accepted species: Selected synonyms include: * '' Ageratum altissimum'' — synonym of '' Ageratina altissima'' * ''

Ageratum anisochroma ''Ageratum'' () (whiteweed in the USA) 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 ...

'' — synonym of '' Ageratina anisochroma'' * ''

Ageratum isocarphoides ''Ageratum'' () (whiteweed in the USA) 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 nativ ...

'' — synonym of '' Ageratum echioides'' * ''

Ageratum lavenia ''Ageratum'' () (whiteweed in the USA) 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 ...

'' — synonym of ''

Adenostemma lavenia ''Adenostemma'' is a genus of flowering plant in the family Asteraceae described as a genus in 1775. It is widespread in tropical regions of Asia, Africa, Australia, the Americas, and various oceanic islands. Species , ''Plants of the World onl ...

'' * ''

Ageratum lucidum ''Ageratum'' () (whiteweed in the USA) 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 ...

'' — synonym of '' Ageratum corymbosum'' * ''

Ageratum meridanum ''Ageratum'' () (whiteweed in the USA) 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 ...

'' — synonym of ''

Ageratum microcarpum ''Ageratum conyzoides'' (billygoat-weed, chick weed, goatweed, whiteweed, mentrasto) is native to Tropical America, especially Brazil, and is an invasive weed in many other regions. It is an herb that is 0.5–1 m. high, with ovate leaves 2–6&n ...

'' * ''

Ageratum nelsonii ''Ageratum'' () (whiteweed in the USA) 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 ...

'' — synonym of '' Ageratum elassocarpum'' * ''

Ageratum oliveri ''Ageratum'' () (whiteweed in the USA) 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 nativ ...

'' — synonym of ''

Ageratum oerstedii ''Ageratum'' () (whiteweed in the USA) 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 ...

'' * '' Ageratum panamense'' — synonym of '' Ageratum riparium'' * '' Ageratum pohlii'' — synonym of '' Teixeiranthus pohlii'' * ''

Ageratum radicans ''Ageratum'' () (whiteweed in the USA) is a genus of 40 to 60 tropical and warm temperate flowering annuals and perennials from the family (biology), family Asteraceae, tribe (biology), tribe Eupatorieae. Most species are native plant, native t ...

'' — synonym of ''

Ageratum peckii ''Ageratum'' () (whiteweed in the USA) 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 ...

'' * ''

Ageratum salicifolium ''Ageratum'' () (whiteweed in the USA) 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 nativ ...

'' — synonym of '' Ageratum corymbosum'' * ''

Ageratum stachyofolium ''Ageratum'' () (whiteweed in the USA) 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 ...

'' — synonym of '' Paneroa stachyofolia''

Segregate genera

The genus ''Paneroa'' consists of one species, ''Paneroa stachyofolia'', native to

Oaxaca ) , population_note = , population_rank = 10th , timezone1 = CST , utc_offset1 = −6 , timezone1_DST = CDT , utc_offset1_DST = −5 , postal_code_type = Postal ...

, which was first described in ''Ageratum'' but which seems to be more closely related to ''

Conoclinium ''Conoclinium'', the mistflowers, is a genus of four species of herbaceous perennial flowering plants, native to North America. They are tall, and have blue to purple or violet flowers (occasionally white). The plants of this genus have someti ...

'' and ''

Fleischmannia ''Fleischmannia'' is a genus of flowering plant in the family Asteraceae. The name honours Gottfried F. Fleischmann (1777–1850), the teacher of Carl Heinrich Schultz at University of Erlangen–Nuremberg. Members of the genus are native to So ...

''.

References

{{Taxonbar, from=Q132653 Asteraceae genera Taxa named by Carl Linnaeus