Eupatorium rotundifolium
Eupatorium sessilifolium
round-leaf boneset, round-leaf thoroughwort, roundleaf eupatorium
upland boneset, upland thoroughwort
(from short rhizomes) single, sparsely branched distally, puberulent.
(from short caudices or rhizomes) single, sparsely branched distally, 5–10+ dm, glabrous or glabrate proximally, puberulent distally (among heads).
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.
usually opposite (distal sometimes alternate); simple, sessile;
blades pinnately nerved, lanceolate to oblong, 70–150+ × 10–30 mm (lengths mostly 2–5 times widths), bases truncate to somewhat rounded, margins serrate, apices narrowly acute to acuminate, faces glabrate (scattered, fine hairs), gland-dotted.
5;
corollas 3–4 mm.
5;
corollas 3–3.5 mm.
8–10 in 2–3 series, elliptic to oblanceolate, 2–6 × 0.5–1.5 mm, apices acute, abaxial faces puberulent, gland-dotted.
10–15 in 2–3 series, elliptic to oblong, 2–5 × 0.5–1.5 mm, apices rounded to acute (not mucronate), abaxial faces villous to puberulent, gland-dotted.
in corymbiform arrays.
in corymbiform arrays.
2–3 mm;
pappi of 30–40 bristles 3.5–4 mm.
2–3 mm;
pappi of 30–40 bristles 3–4 mm.
= 20, 30.
Eupatorium rotundifolium
Eupatorium sessilifolium
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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