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

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Asteraceae,

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

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

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

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 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 Bedding, also called bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative effect. Bedding is the removable and washable portion of a human sleeping environment ...

, 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 The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

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, growing where it conflicts with human preferences, needs, or goals.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. Pla ...

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'' – synonym of '' Ageratina anisochroma'' * '' Ageratum isocarphoides'' – synonym of '' Ageratum echioides'' * '' Ageratum lavenia'' – synonym of '' Adenostemma lavenia'' * '' Ageratum lucidum'' – synonym of '' Ageratum corymbosum'' * '' Ageratum meridanum'' – synonym of '' Ageratum microcarpum'' * '' Ageratum nelsonii'' – synonym of '' Ageratum elassocarpum'' * '' Ageratum oliveri'' – synonym of '' Ageratum oerstedii'' * ''

Ageratum panamense ''Ageratum'' () (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 ...

'' – synonym of '' Ageratum riparium'' * '' Ageratum pohlii'' – synonym of '' Teixeiranthus pohlii'' * '' Ageratum radicans'' – synonym of '' Ageratum peckii'' * '' Ageratum salicifolium'' – synonym of '' Ageratum corymbosum'' * '' Ageratum stachyofolium'' – synonym of '' Paneroa stachyofolia''

Segregate genera

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

Oaxaca Oaxaca, officially the Free and Sovereign State of Oaxaca, is one of the 32 states that compose the political divisions of Mexico, Federative Entities of the Mexico, United Mexican States. It is divided into municipalities of Oaxaca, 570 munici ...

, which was first described in ''Ageratum'' but which seems to be more closely related to '' Conoclinium'' and '' Fleischmannia''.

References

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