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white thoroughwort

Habit Perennials, 40–100+ cm.
Stems

(from short caudices or stout rhizomes) single, sparsely branched distally, pubescent throughout.

Leaves

usually opposite (distal sometimes alternate);

sessile;

blades ± 3-nerved or pinnately nerved, elliptic to oblanceolate, 30–120 × 10–40 mm (lengths mostly 3–4 times widths), bases narrowly cuneate (sometimes oblique), margins subentire, serrate, or serrulate, apices rounded to acute, faces setulose (denser on midribs and veinlets) to glabrate, usually gland-dotted.

Florets

(4–)5;

corollas 4–4.5 mm.

Phyllaries

9–15 in 2–4 series, linear, 1.5–9 × 0.6–1 mm, apices acuminate to attenuate, sometimes mucronate, abaxial faces pubescent throughout, gland-dotted.

Heads

in corymbiform arrays.

Cypselae

2.5–3.5 mm;

pappi of 40–50 bristles 3.5–4.5 mm.

Eupatorium album

Distribution
from FNA
AL; CT; DC; DE; FL; GA; KY; LA; MD; MS; NC; NJ; NY; OH; PA; SC; TN; VA; WV
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Discussion

Varieties 3 (3 in the flora).

Eupatorium album is represented by widespread diploid populations and by polyploid, apomictic populations, segregated as varieties, that may have arisen by hybridization with other species. Molecular data suggest that var. vaseyi arose via hybridization between var. album and E. sessilifolium. They also suggest that E. album var. subvenosum arose from hybridization between E. album var. album and E. serotinum.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key
1. Leaf blades: margins coarsely serrate, apices obtuse to rounded, faces pubescent
var. album
1. Leaf blades: margins subentire, serrulate, or serrate, apices acute, faces pubescent to glabrate
→ 2
2. Leaf blades 3-nerved from bases, 40–70 × 10–20 mm, margins subentire to serrulate
var. subvenosum
2. Leaf blades 3-nerved distal to bases, 50–110 × 20–40 mm, margins evenly serrate
var. vaseyi
Source FNA vol. 21, p. 465.
Parent taxa Asteraceae > tribe Eupatorieae > Eupatorium
Sibling taxa
E. altissimum, E. anomalum, E. cannabinum, E. capillifolium, E. compositifolium, E. godfreyanum, E. hyssopifolium, E. lancifolium, E. leptophyllum, E. leucolepis, E. linearifolium, E. mikanioides, E. mohrii, E. perfoliatum, E. petaloideum, E. pilosum, E. resinosum, E. rotundifolium, E. semiserratum, E. serotinum, E. sessilifolium, E. ×cordigerum, E. ×pinnatifidum
Subordinate taxa
E. album var. album, E. album var. subvenosum, E. album var. vaseyi
Name authority Linnaeus: Mant. Pl., 111. (1767): Syst. Nat. ed. 12, 2: 536. (1767)
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