Flora of North America species comparison

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Eupatorium mohrii

Eupatorium petaloideum

Mohr's thoroughwort

showy white thoroughwort
Habit Perennials, 30–100+ cm. Perennials, 30–70 cm.
Stems

(from tuberous rhizomes) multiple, densely branched distally, puberulent throughout.

(from short, stout rhizomes) single, branched distally, puberulent.
Leaves

usually opposite (distal sometimes alternate);

sessile or subsessile;

blades 3-nerved distal to bases, oblanceolate, 20–80 × 5–10(–20) mm, bases cuneate, margins serrate proximally, entire distally, apices acute, faces puberulent (abaxial), glabrous or glabrate (adaxial), gland-dotted.

usually opposite (distal sometimes alternate);

sessile;

blades pinnately nerved, elliptic to ovate, 20–80 × 10–30 mm, bases cuneate, margins serrate to crenate-serrate, apices rounded to acute, faces sparsely villous (abaxial), glabrate (adaxial), little, if at all, gland-dotted.
Florets

5;

corollas 2–4 mm.

(4–)5;

corollas 3–3.5 mm.
Phyllaries

7–10 in 1–2 series, oblanceolate, 1–3 × 0.2–0.5 mm, apices rounded, abaxial faces puberulent, gland-dotted.

9–15 in 2–4 series, linear, 4–10 × 0.6–1 mm, apices (white) acuminate to attenuate, strongly mucronate, abaxial faces glabrous, not gland-dotted.
Heads

in corymbiform arrays.

in corymbiform arrays.
Cypselae

1–2 mm;

pappi of 20–30 bristles 2.5–3 mm.

2.5–3 mm;

pappi of 40–50 bristles 3.5–4 mm.
2n

= 20, 30, 40.

= 20.

Eupatorium mohrii

Eupatorium petaloideum
Phenology Flowering Jul–Sep. Flowering Jul–Sep.
Habitat Moist, low ground, margins of ponds, sandy soils Upland scrub oak and longleaf pinewoods, fine textured, loamy soils
Elevation 10–100+ m (0–300+ ft) 20–100+ m (100–300+ ft)
Distribution
from FNA
AL; FL; GA; LA; MS; NC; SC; TX; VA
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; FL; GA; MS
[BONAP county map]
Discussion

As treated here, Eupatorium mohrii includes both sexual diploid (sometimes segregated as E. recurvans) and apomictic polyploid populations that are suggested by molecular data to be autoploids. Eupatorium saltuense refers to hybrids shown by molecular data to involve E. mohrii and E. serotinum. Molecular data also document frequent hybridization with E. rotundifolium.

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

Eupatorium petaloideum is commonly combined with E. album; it has recently been separated as a distinct variety. V. I. Sullivan (1972) found the two taxa to be distinct chemically and to occupy different habitats. In both, the involucral bracts are white and long-acuminate or mucronate; those of E. petaloideum are almost entirely devoid of any pubescence including glands and those of E. album have both simple and glandular hairs.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 21, p. 470. FNA vol. 21, p. 471.
Parent taxa Asteraceae > tribe Eupatorieae > Eupatorium Asteraceae > tribe Eupatorieae > Eupatorium
Sibling taxa
E. album, 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. perfoliatum, E. petaloideum, E. pilosum, E. resinosum, E. rotundifolium, E. semiserratum, E. serotinum, E. sessilifolium, E. ×cordigerum, E. ×pinnatifidum
E. album, 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. pilosum, E. resinosum, E. rotundifolium, E. semiserratum, E. serotinum, E. sessilifolium, E. ×cordigerum, E. ×pinnatifidum
Synonyms E. recurvans E. album var. petaloideum
Name authority Greene: Contr. U.S. Natl. Herb. 6: 762, plate 11. (1901) Britton: Bull. Torrey Bot. Club 24: 492. (1897)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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