Eupatorium rotundifolium
Eupatorium leptophyllum
round-leaf boneset, round-leaf thoroughwort, roundleaf eupatorium
false fennel
(from short rhizomes) single, sparsely branched distally, puberulent.
(from short caudices) single, branched distally, glabrous throughout, gland-dotted.
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 (nodes often appearing leafy by development of leaves on lateral buds without axis elongation); petiolate or sessile;
blades (usually pinnately or ternately lobed) or lobes 1-nerved or pinnately nerved, linear, 20–100 × 0.2–0.5(–1) mm, bases slightly expanded, margins entire, apices rounded to acute, faces sparsely puberulent to glabrate, gland-dotted.
5;
corollas 3–4 mm.
5;
corollas 2–2.5 mm.
8–10 in 2–3 series, elliptic to oblanceolate, 2–6 × 0.5–1.5 mm, apices acute, abaxial faces puberulent, gland-dotted.
6–10 in 1–2 series, lanceolate, 1.5–3 × 0.5–0.7 mm, apices acuminate, mucronate, abaxial faces glabrous or glabrate (not gland-dotted).
in corymbiform arrays.
in paniculiform arrays (branches supporting heads recurved, secund).
2–3 mm;
pappi of 30–40 bristles 3.5–4 mm.
1–1.5 mm;
pappi of 15–30 bristles 2–2.5 mm.
= 20.
Eupatorium rotundifolium
Eupatorium leptophyllum
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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