''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 Native may refer to: People * '' Jus sanguinis'', nationality by blood * '' Jus soli'', nationality by location of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Nat ...

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 In botany, phyllotaxis () or phyllotaxy is the arrangement of leaf, leaves on a plant stem. Phyllotactic spirals form a distinctive class of patterns in nature. Leaf arrangement The basic leaf#Arrangement on the stem, arrangements of 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 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 subst ...

, containing

pyrrolizidine alkaloids Pyrrolizidine alkaloids (PAs), sometimes referred to as necine bases, are a group of naturally occurring alkaloids based on the structure of pyrrolizidine. Their use dates back centuries and is intertwined with the discovery, understanding, and ...

. ''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 A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...

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 ''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 ''

Ageratina anisochroma ''Ageratina'', commonly known as snakeroot, is a genus of over 300 species of perennials and rounded shrubs in the family Asteraceae. These plants grow mainly in the warmer regions of the Americas and West Indies. Over 150 species are native to ...

'' * '' Ageratum isocarphoides'' – synonym of ''

Ageratum echioides ''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 ...

'' * '' Ageratum lavenia'' – synonym of '' Adenostemma lavenia'' * '' Ageratum lucidum'' – synonym of ''

Ageratum corymbosum ''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 ...

'' * '' Ageratum meridanum'' – synonym of '' Ageratum microcarpum'' * '' Ageratum nelsonii'' – synonym of ''

Ageratum elassocarpum ''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 ...

'' * '' 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 ''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 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 ''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 sometim ...

'' 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 Sou ...

''.

References

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