Ageratina altissima (Linnaeus) R.M. King & H. Robinson. Common name: Common White Snakeroot, Common Milk-poison. Phenology: Late Jul-Nov. Habitat: Moist forests, such as cove forests. Mesic forests, successional and disturbed forests, old fields. Distribution: QC west to se. ND, south to Panhandle FL and c. TX.
Origin/Endemic status: Native
Taxonomy Comments: Var. angustata (A. Gray) Clewell & Wooten is sometimes recognized, and ranges from IL and e. KS south to LA and c. TX.
Other Comments: This species has been shown to be the cause of the "milk sickness" of pioneer days; the plants contain a poison which is transmissible to humans through cow milk.
Synonymy ⓘ: = K4, Lamont (2018); = Ageratina altissima (L.) R.M.King & H.Rob. var. altissima — Ar, Can, FNA21, NE, NY, Pa, Tn, Va; = Eupatorium rugosum Houtt. var. rugosum — C, SE1; = Eupatorium urticifolium Reichard — S; < Ageratina altissima (L.) R.M.King & H.Rob. — Fl7, Il, Mi, Ok, WH3; >< Ageratina altissima (L.) R.M.King & H.Rob. var. altissima — Clewell & Wooten (1971); > Ageratina altissima (L.) R.M.King & H.Rob. var. angustata (A.Gray) Blake — Clewell & Wooten (1971); < Eupatorium rugosum Houtt. — G, GrPl, NcTx, Oh3, RAB, Tat, Tx, W; > Eupatorium rugosum Houtt. var. chlorolepis Fernald — F; > Eupatorium rugosum Houtt. var. rugosum — F; > Eupatorium rugosum Houtt. var. tomentellum (B.L.Rob.) Blake — F; Ageratum altissimum Linnaeus. Basionym: Ageratum altissimum L. 1753
Links to other floras: = Ageratina altissima var. altissima - FNA21
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Wetland Indicator Status:
- Atlantic and Gulf Coastal Plain: FACU
- Eastern Mountains and Piedmont: FACU
- Great Plains: UPL
- Midwest: FACU
- Northcentral & Northeast: FACU
Heliophily ⓘ: 3
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© Keith Bradley | Original Image ⭷
© Richard & Teresa Ware CC-BY-NC, permission granted to NCBG | Original Image ⭷
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© Gary P. Fleming | Original Image ⭷
© Erik Danielson source | Original Image ⭷
© Keith Bradley | Original Image ⭷
© Joey Shaw source | Original Image ⭷
© Richard & Teresa Ware CC-BY-NC, permission granted to NCBG | Original Image ⭷Feedback
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Horticultural Information
Intro: Erect perennial of moist, deciduous forests such as cove forests.
Stems: Stems 1-several, many-branched, smooth to hairy, sometimes whitish.
Leaves: Leaves opposite, long-petiolate, oval to lance-shaped and rounded to somewhat wedge-shaped at base, 2-7 in. long, with 3 major veins arising from base, toothed and smooth.
Inforescence:
Flowers: Composite flowers (heads) arranged in branching terminal and upper axillary clusters; heads white, about 1/3 in. tall, consisting of 9-30 tubular disk florets surrounded by 2 series of narrow bracts; protruding styles give heads a fuzzy appearance.
Fruits:
Comments: Two varieties of Ageratina altissima are now recognized. Var. roanensis differs from var. altissima in having inflorescences with more heads, slightly larger bracts, and triangular leaves (leaf base tending toward flat); it is known from higher elevations in the s. Blue Ridge Mountains.
Height: 1 1/2-4 ft.
plant sale text: <span style="color: #ff0000;"> Warning - This plant is highly toxic if eaten, so please keep it away from children and pets. </span> Formerly classified as Eupatorium rugosum, this species is more shade tolerant than other species in the genus. This species has an exceptionally long bloom season, and the clusters of small, fragrant white flowers will attract butterflies, bees, and other pollinators. White Snakeroot spreads by rhizomatous roots to form colonies and will also self-seed. Settlers who drank milk from cows that fed on this plant often developed the disease called milk sickness.
bloom table text:
description: Erect perennial of moist, deciduous forests such as cove forests.
stems: Stems 1-several, many-branched, smooth to hairy, sometimes whitish.
leaves: Leaves opposite, long-petiolate, oval to lance-shaped and rounded to somewhat wedge-shaped at base, 2-7 in. long, with 3 major veins arising from base, toothed and smooth.
inflorescence:
flowers: Composite flowers (heads) arranged in branching terminal and upper axillary clusters; heads white, about 1/3 in. tall, consisting of 9-30 tubular disk florets surrounded by 2 series of narrow bracts; protruding styles give heads a fuzzy appearance.
fruits:
comments: Two varieties of Ageratina altissima are now recognized. Var. roanensis differs from var. altissima in having inflorescences with more heads, slightly larger bracts, and triangular leaves (leaf base tending toward flat); it is known from higher elevations in the s. Blue Ridge Mountains.
cultural notes:
germination code:
native range: central & eastern N. America
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