Eupatorium linearifolium
Eupatorium petaloideum
waxy thoroughwort
showy white thoroughwort
(from short caudices) single or multiple, branched at or near bases, pubescent throughout.
(from short, stout rhizomes) single, branched distally, puberulent.
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 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.
5;
corollas 3–3.5 mm.
(4–)5;
corollas 3–3.5 mm.
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.
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.
in corymbiform arrays.
in corymbiform arrays.
2.5–3 mm;
pappi of 30–40 bristles 3–5 mm.
2.5–3 mm;
pappi of 40–50 bristles 3.5–4 mm.
= 20, 30, 40.
= 20.
Eupatorium linearifolium
Eupatorium petaloideum
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 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.)
WildflowerSearch
iNaturalist
USDA Plants Database
