Eupatorium album
Eupatorium rotundifolium
white thoroughwort
round-leaf boneset, round-leaf thoroughwort, roundleaf eupatorium
(from short caudices or stout rhizomes) single, sparsely branched distally, pubescent throughout.
(from short rhizomes) single, sparsely branched distally, puberulent.
usually opposite (distal sometimes alternate);
sessile;
blades ± 3-nerved or pinnately nerved, elliptic to oblanceolate, 30–120 × 10–40 mm (lengths mostly 3–4 times widths), bases narrowly cuneate (sometimes oblique), margins subentire, serrate, or serrulate, apices rounded to acute, faces setulose (denser on midribs and veinlets) to glabrate, usually 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.
(4–)5;
corollas 4–4.5 mm.
5;
corollas 3–4 mm.
9–15 in 2–4 series, linear, 1.5–9 × 0.6–1 mm, apices acuminate to attenuate, sometimes mucronate, abaxial faces pubescent throughout, gland-dotted.
8–10 in 2–3 series, elliptic to oblanceolate, 2–6 × 0.5–1.5 mm, apices acute, abaxial faces puberulent, gland-dotted.
in corymbiform arrays.
in corymbiform arrays.
2.5–3.5 mm;
pappi of 40–50 bristles 3.5–4.5 mm.
2–3 mm;
pappi of 30–40 bristles 3.5–4 mm.
Eupatorium album
Eupatorium rotundifolium
Varieties 3 (3 in the flora).
Eupatorium album is represented by widespread diploid populations and by polyploid, apomictic populations, segregated as varieties, that may have arisen by hybridization with other species. Molecular data suggest that var. vaseyi arose via hybridization between var. album and E. sessilifolium. They also suggest that E. album var. subvenosum arose from hybridization between E. album var. album and E. serotinum.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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: margins coarsely serrate, apices obtuse to rounded, faces pubescent | var. album |
1. Leaf blades: margins subentire, serrulate, or serrate, apices acute, faces pubescent to glabrate | → 2 |
2. Leaf blades 3-nerved from bases, 40–70 × 10–20 mm, margins subentire to serrulate | var. subvenosum |
2. Leaf blades 3-nerved distal to bases, 50–110 × 20–40 mm, margins evenly serrate | var. vaseyi |
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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