Eupatorium rotundifolium
Eupatorium compositifolium
round-leaf boneset, round-leaf thoroughwort, roundleaf eupatorium
dogfennel eupatorium, yankeeweed
(from short rhizomes) single, sparsely branched distally, puberulent.
(from short caudices) single, branched distally, puberulent throughout (lateral buds often develop fertile and infertile branches).
usually opposite (distal sometimes alternate, lateral buds dormant or producing 1 pair of leaves);
sessile or subsessile;
blades ± 3-nerved, usually ± deltate to orbiculate, sometimes ovate, 15–50(–70) × 15–40(–60) mm (lengths mostly 1–2 times widths), bases broadly rounded to truncate, margins crenate to serrate, apices acute, faces puberulent to villous, gland-dotted.
opposite (proximal) or alternate (lateral buds dormant or producing 1 pair of leaves);
sessile;
blades (often pinnately or ternately lobed) or lobes pinnately nerved, linear, 20–80 × 0.5–2.5(–4) mm, bases cuneate, margins entire, apices acuminate, faces puberulent, gland-dotted.
5;
corollas 3–4 mm.
5;
corollas (sometimes with purple throats) 2.5–3 mm.
8–10 in 2–3 series, elliptic to oblanceolate, 2–6 × 0.5–1.5 mm, apices acute, abaxial faces puberulent, gland-dotted.
7–10 in 2–3 series, (sometimes purple) elliptic to oblong, 1–3 × 0.5–0.8 mm, (margins hyaline) apices acuminate and mucronate, abaxial faces puberulent (mostly on midveins), usually gland-dotted.
in corymbiform arrays.
in paniculiform arrays.
2–3 mm;
pappi of 30–40 bristles 3.5–4 mm.
1–1.7 mm;
pappi of 20–30 bristles 3–3.5 mm.
= 20.
Eupatorium rotundifolium
Eupatorium compositifolium
Varieties 3 (3 in the flora).
Eupatorium rotundifolium is one of the more variable species of the genus; its apparent propensity to hybridize with other species has led it to be described as a compilospecies and has complicated its delimitation. Hybrids with E. perfoliatum and E. sessilifolium are sufficiently distinctive to be treated here as distinctive entities (E. ×cordigerum and E. godfreyanum, respectively), and the varieties ovatum and scabridum have also been proposed to be of hybrid origin. The boundaries between varieties are indistinct and individual specimens may be difficult to place with confidence.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaf blades 3-nerved from bases, bases subtruncate to broadly cuneate, margins crenate | var. rotundifolium |
1. Leaf blades 3-nerved distal to bases, bases broadly cuneate to cuneate, margins serrate | → 2 |
2. Leaf blades 30–70 × 30–60 mm, broadest nearmiddles | var. ovatum |
2. Leaf blades 20–50 × 15–30 mm, broadest nearbases | var. scabridum |
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