The common name of this species derives from the erroneous belief among early settlers that the bitter rhizomes were beneficial in the treatment of snakebites. In fact, the foliage and rhizomes are highly toxic, causing fatalities from 'Milk Sickness' because the toxins can pass through the milk of dairy cattle to humans. White Snakeroot has been reassigned recently to the genus Ageratina, although it is still often referred to as Eupatorium rugosum. Normally, White Snakeroot is largely hairless, although some authorities describe a pubescent variety of this species. White Snakeroot resembles many of the white-flowered Eupatorium spp. (Bonesets), but these different species can be distinguished from each other by the appearance of their leaves. Among the species in this group, White Snakeroot has the broadest leaves; its lower leaves are cordate or broadly ovate, and these leaves have long petioles. White Snakeroot usually occurs in and around shady woodlands, while many of these other species are found in prairies and sunny wetlands.

This native perennial plant is about 1½–3' tall, branching occasionally. The light green to tan stems are round and largely hairless. The opposite leaves are up to 6' long and 3½' across, becoming smaller as they ascend the stems. The lower leaves are cordate to cordate-ovate, while the upper leaves are broadly lanceolate to lanceolate. All of the leaves are largely hairless and strongly serrated along the margins. There are 3 prominent veins on the upper surface of each leaf (particularly the lower ones), while the lower surface has an elevated network of veins. The rather long petioles are ½–2½' in length. The upper stems terminate in compound corymbs of flowerheads that span several inches across. Each flowerhead is about ½' across and contains 10-30 disk florets that are brilliant white. There are no ray florets. Each disk floret is about 1/5' across when fully open; it consists of a small tubular corolla with 5 lobes that are spreading and pointed, and it has a divided style that is strongly exerted from the corolla. At the base of each flowerhead, there is a single series of linear floral bracts that are green and non-overlapping. The blooming period occurs from late summer through the fall and lasts about 2 months. This is one of the last wildflowers to bloom during the fall. The flowers are often fragrant. Each disk floret is replaced by a dark linear achene with a small tuft of white hairs. These achenes are distributed by the wind. The root system consists of spreading rhizomes and shallow fibrous roots. This plant can spread vegetatively by means of its rhizome, or it can reseed itself into new areas.

Ageratina altissima pollen has tricolporate apertures with echinate ornamentation. (Jones & Wilson, 2001.)

Ageratina altissima was first described as Ageratum altissimum by Linnaeus in Species Plantarum, Vol. 2, in 1753. In 1970, R.M. King and H. Robinson reviewed the classification and renamed it under the epithet Ageratina altissima with two varieties, var. altissima and var. roanensis.

A. altissima is a perennial herb with an upright stem and clustered, white flower heads. Var. roanensis, known as the Appalachian white snakeroot, has slightly longer phyllaries with cuspidated apices. Its growth is mostly limited to the southeastern U.S. Var. altissima grows throughout the entire eastern U.S. and southeastern Canada.

White Snakeroot is a common plant that occurs in almost every county in Illinois (see Distribution Map); it is quite likely that this species occurs in every county. Habitats include moist to slightly dry deciduous woodlands, woodland borders, thickets, partially shaded to shady seeps, bluffs, woodland meadows along rivers, powerline clearances in woodlands, shady corners of pastures and yards, fence rows with woody vegetation, and overgrown vacant lots. This species is especially common in wooded areas that are rather disturbed and degraded, although it also occurs at higher quality sites.

Eupatorium rugosum var. rugosum :
Canada (North America)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Eupatorium rugosum fo. rugosum :
Canada (North America)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Ageratina altissima (L.) R.M. King & H. Rob.:
China (Asia)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

As a species, Ageratina altissima spans the entirety of the eastern and midwestern United States, in addition to the corresponding southcentral to southeastern parts of Canada. A. altissima var. altissima is found throughout the entire range, with the exclusion of Georgia. A. altissima var. roanensis is isolated to the southeastern U.S. excluding coasts. (Nesom, 2006.)

For more information, see the maps above provided by Flora of North America.

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

The key to the varieties below is taken from Flora of North America. (Nesom, 2006.)

1. Phyllaries 3-5 mm, apices not cuspidate..............................................1a. Ageratina altissima var. altissima

1. Phyllaries 4-7 mm, apices cuspidate to acuminate.............................1b. Ageratina altissima var. roanensis

Perennials, (30–)50–80(–120) cm (bases usually fibrous-rooted crowns, sometimes rhizomatous). Stems ascending to erect, sometimes semiscandent, puberulent (hairs minute, crisped). Leaves opposite; petioles (5–)10–30(–50) mm; blades usually deltate-ovate to ovate or broadly lanceolate, sometimes ovate-lanceolate, 4–11(–13) × 2.5–8(–9) cm, bases usually rounded to truncate or obtuse, sometimes cordate, margins coarsely and doubly incised-serrate, apices usually acuminate. Heads clustered. Peduncles 1–5 mm, puberulent. Involucres 4–5 mm. Phyllaries: apices acute, abaxial faces glabrous or sparsely and finely villous. Corollas white, lobes sparsely short-villous. Cypselae glabrous.

Ageratum altissimum Linnaeus, Sp. Pl. 2: 839. 1753, not Eupatorium altissimum Linnaeus 1753

"Perennials, (30–)50–80(–120) cm (bases usually fibrous-rooted crowns, sometimes rhizomatous). Stems ascending to erect, sometimes semiscandent, puberulent (hairs minute, crisped). Leaves opposite; petioles (5–)10–30(–50) mm; blades usually deltate-ovate to ovate or broadly lanceolate, sometimes ovate-lanceolate, 4–11(–13) × 2.5–8(–9) cm, bases usually rounded to truncate or obtuse, sometimes cordate, margins coarsely and doubly incised-serrate, apices usually acuminate. Heads clustered. Peduncles 1–5 mm, puberulent. Involucres 4–5 mm. Phyllaries: apices acute, abaxial faces glabrous or sparsely and finely villous. Corollas white, lobes sparsely short-villous. Cypselae glabrous."

Nesom, Guy Ageratina" in Flora of North America, Vol. 21, p. 547-553. Oxford University Press, Inc., New York, NY. 2006.

White Snakeroot is a common plant that occurs in almost every county in Illinois (see Distribution Map); it is quite likely that this species occurs in every county. Habitats include moist to slightly dry deciduous woodlands, woodland borders, thickets, partially shaded to shady seeps, bluffs, woodland meadows along rivers, powerline clearances in woodlands, shady corners of pastures and yards, fence rows with woody vegetation, and overgrown vacant lots. This species is especially common in wooded areas that are rather disturbed and degraded, although it also occurs at higher quality sites.

Both varieties of Ageratina altissima thrive in moist cove forests. Var. altissima is found at an altitude of 10-800 m, whereas var. roanensis prefers a higher altitude between 700-1500 m. (Nesom, 2006.)

Like other composites, its fruit is an achene and it is dispersed with the help of the wind.

The nectar of the flowers attracts a variety of insects, including large Leaf-Cutting bees, Halictid bees, wasps, various flies (Syrphid, Tachinid, Bee flies, & others), butterflies, and moths. The bees also collect pollen. The caterpillars of some moths are known to feed on Eupatorium spp. (Bonesets), including White Snakeroot (probably). These species include Carmenta bassiformis (Eupatorium Borer Moth), Papaipema cataphracta (Burdock Borer Moth), Phragmatobia fuliginosa (Ruby Tiger Moth), and Phragmatobia lineata (Lined Ruby Tiger Moth). Because the foliage is bitter and toxic, mammalian herbivores avoid this plant as a food source. Sometimes cattle will eat it in overgrazed pastures, which can produce fatal results.

Ageratina altissima (White Snakeroot)
(Also called Eupatorium rugosum; bees suck nectar or collect pollen, flies suck nectar or feed on pollen, other insects suck nectar; some observations are from Graenicher as indicated below, otherwise they are from Robertson)

Bees (long-tongued)
Apidae (Apinae): Apis mellifera sn cp fq (Rb, Gr); Apidae (Bombini): Bombus griseocallis sn (Gr), Bombus vagans sn cp (Gr); Anthophoridae (Ceratinini): Ceratina dupla dupla sn (Gr); Megachilidae (Megachilini): Megachile centuncularis sn cp (Gr), Megachile latimanus sn cp (Rb, Gr), Megachile mendica sn cp (Rb, Gr)

Bees (short-tongued)
Halictidae (Halictinae): Agapostemon sericea sn (Gr), Augochlorella striata sn, Halictus (or Lasioglossum) sp. sn cp (Gr), Halictus confusus sn cp (Rb, Gr), Halictus ligatus sn cp fq, Lasioglossum coriaceus sn (Gr), Lasioglossum imitatus sn, Lasioglossum versatus sn cp (Gr), Lasioglossum zephyrus sn cp (Gr); Colletidae (Colletinae): Colletes compactus sn (Gr)

Wasps
Sphecidae (Larrinae): Ancistromma distincta; Sphecidae (Sphecinae): Sphex ichneumonea (Gr); Scoliidae: Scolia bicincta (Rb, Gr); Vespidae: Dolichovespula maculata, Vespula germanica; Vespidae (Eumeninae): Ancistrocerus adiabatus (Rb, Gr)

Flies
Culicidae: Aedes vexans (Gr); Scathophagidae: Scathophaga furcata (Gr); Syrphidae: Allograpta obliqua sn (Rb, Gr), Eristalis arbustorum (Gr), Eristalis brousii (Gr), Eristalis dimidiatus (Gr), Eristalis tenax (Gr), Eristalis transversus (Gr), Helophilus fasciatus (Gr), Paragus tibialis (Gr), Rhingia nasica, Spilomyia fusca (Gr), Spilomyia longicornis sn (Rb, Gr), Syritta pipiens (Gr), Syrphus ribesii sn (Rb, Gr), Toxomerus geminatus (Gr), Tropidia quadrata (Gr); Bombyliidae: Anthrax oedipus (Gr), Exoprosopa fasciata sn, Sparnopolius confusus (Gr); Tachinidae: Archytas analis (Gr), Estheria abdominalis sn, Gymnoclytia immaculata (Gr), Gymnoclytia occidua sn, Gymnosoma fuliginosum (Gr), Paradidyma singularis sn, Phyllomya cremides (Gr); Anthomyiidae: Delia platura (Gr); Calliphoridae: Lucilia illustris (Gr), Lucilia sericata (Gr); Muscidae: Graphomya maculata (Gr), Musca domestica (Gr), Neomyia cornicina sn, Stomoxys calcitrans (Gr)

Butterflies
Nymphalidae: Limenitis archippus (Gr), Phyciodes tharos (Gr), Speyeria aphrodite aphrodite (Gr); Lycaenidae: Celastrina argiolus

Skippers
Hesperiidae: Ancyloxypha numitor (Gr)

Moths
Ctenuchidae: Cisseps fulvicollis; Noctuidae: Anagrapha falcifera (Gr); Tortricidae: Grapholita interstinctana (Gr)

Beetles
Chrysomelidae: Acalymma vittata (Gr), Epitrix cucumeris (Gr); Curculionidae: Hypera punctata (Gr)

Plant Bugs
Miridae: Lygus lineolaris (Gr), Plagiognathus sp. (Gr)

Ageratina altissima has nectar that attracts a variety of moths, butterflies, wasps, flies and bees. Some caterpillars may feed on its foliage. Mammals usually avoid it due to the bitter taste of the toxic compounds within.

Both varieties can be found flowering late summer, July to October.

Perennial

Recent studies indicate that there may be three distinct chemotypes of Ageratina altissima. In addition to tremetol, six previously unrecorded compounds of varying toxicity have been found in an extract from the plant. It is thought that this variation could be responsible for the sporadic poisoning associated with A. altissima. (Lee et. al., 2010)

Ageratina altissima has a chromosome number around 17. (King, Kyhos, Powell, Raven & Robinson, 1972.)

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

The preference is partial sun to light shade, moist to slightly dry conditions, and a soil that is loamy, slightly rocky, or slightly gravelly. This plant dislikes too much sun, otherwise it is easy to grow.

Occasionally large mammals will try it, resulting in illness or death. Consequently, humans who consume the milk of an animal that has eaten A. altissima can also get sick and die.