Flora of North America species comparison

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Eupatorium linearifolium

Eupatorium ×cordigerum

waxy thoroughwort
Habit Perennials, 30–100+ cm. Perennials, 40–100+ cm.
Stems

(from short caudices) single or multiple, branched at or near bases, pubescent throughout.

(from short rhizomes) single, branched distally, densely pilose.
Leaves

usually opposite (distal sometimes alternate);

sessile or subsessile;

blades 3-nerved distal to bases, oblong to lance-oblong, 20–45 × 5–10 mm, bases cuneate, margins entire or serrate (teeth mostly proximal), apices acute, faces finely puberulent, gland-dotted.

usually opposite (distal sometimes alternate);

sessile;

blades ± 3-nerved or pinnately nerved, ovate, 3–9.8 × 1.6–5.7 cm, bases clasping or narrowly perfoliate, margins serrate, apices acute, faces (rugose) sparsely pilose (adaxial) or densely pilose (abaxial) and densely gland-dotted.
Florets

5;

corollas 3–3.5 mm.

5–8;

corollas 2.5–3 mm.
Phyllaries

8–10 in 1–2 series, lanceolate (tapering toward apices), 2–5 × 0.5–1 mm, apices rounded to acute, abaxial faces puberulent, gland-dotted.

7–10 in 2–3 series, 4–12 × 1–4 mm, apices (usually white) acuminate to acute, abaxial faces pilose, gland-dotted.
Heads

in corymbiform arrays.

in corymbiform arrays.
Cypselae

2.5–3 mm;

pappi of 30–40 bristles 3–5 mm.

2–3 mm;

pappi of 30–40 bristles 3.5–4.5 mm.
2n

= 20, 30, 40.

= 30, 40.

Eupatorium linearifolium

Eupatorium ×cordigerum
Phenology Flowering Jul–Sep. Flowering Jul–Aug.
Habitat Dry, sandy soils, pine and oak woods, old fields Margins of woods, moist areas
Elevation 20–100+ m (100–300+ ft) 10–100+ m (0–300+ ft)
Distribution
from FNA
AL; DE; FL; GA; MS; NC; SC; TX
[WildflowerSearch map]
[BONAP county map]
from FNA
AR; MS; NC; NJ; SC; VA
[BONAP county map]
Discussion

Plants treated here as Eupatorium linearifolium were long treated under the name E. cuneifolium; the latter name was superfluous when published (K. N. Gandhi and R. D. Thomas 1991). Because there appears to be a continuous range of variation between diploids that were referred to by V. I. Sullivan (1972) as E. cuneifolium and the series of putative hybrids (with E. hyssopifolium suggested as the other parent) that she called E. linearifolium, these are combined here. The tendency for the plants to branch at or near the bases is distinctive within Eupatorium.

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

Eupatorium ×cordigerum is an apomictic, polyploid hybrid of E. rotundifolium and E. perfoliatum that occurs in disturbed areas where those two species occur together. It is not uncommonly encountered; it is unclear how long it persists.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 21, p. 470. FNA vol. 21, p. 467.
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. mikanioides, E. mohrii, 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. petaloideum, E. pilosum, E. resinosum, E. rotundifolium, E. semiserratum, E. serotinum, E. sessilifolium, E. ×pinnatifidum
Synonyms E. cuneifolium, E. glaucescens, E. tortifolium E. rotundifolium var. cordigerum
Name authority Walter: Fl. Carol., 199. (1788) (Fernald) Fernald: Rhodora 47: 192. (1945)
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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