Ageratina altissima

(Linnaeus) R. M. King & H. Robinson
Phytologia 19: 212. 1970.
Common names: White snakeroot
Basionym: Ageratum altissimum Linnaeus
Treatment appears in FNA Volume 21. Treatment on page 549. Mentioned on page 548, 550, 551.
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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.


Varieties 2 (2 in the flora).

Selected References



1 Phyllaries 3–5 mm, apices not cuspidate Ageratina altissima var. altissima
1 Phyllaries 4–7 mm, apices cuspidate to acuminate Ageratina altissima var. roanensis