Eupatorium rotundifolium |
Eupatorium ×cordigerum |
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round-leaf boneset, round-leaf thoroughwort, roundleaf eupatorium |
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Habit | Perennials, 40–100+ cm. | Perennials, 40–100+ cm. | ||||||||
Stems | (from short rhizomes) single, sparsely branched distally, puberulent. |
(from short rhizomes) single, branched distally, densely pilose. |
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Leaves | 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); sessile; blades ± 3-nerved or pinnately nerved, ovate, 3–9.8 × 1.6–5.7 cm, bases clasping or narrowly perfoliate, margins serrate, apices acute, faces (rugose) sparsely pilose (adaxial) or densely pilose (abaxial) and densely gland-dotted. |
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Florets | 5; corollas 3–4 mm. |
5–8; corollas 2.5–3 mm. |
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Phyllaries | 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, 4–12 × 1–4 mm, apices (usually white) acuminate to acute, abaxial faces pilose, gland-dotted. |
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Heads | in corymbiform arrays. |
in corymbiform arrays. |
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Cypselae | 2–3 mm; pappi of 30–40 bristles 3.5–4 mm. |
2–3 mm; pappi of 30–40 bristles 3.5–4.5 mm. |
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2n | = 30, 40. |
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Eupatorium rotundifolium |
Eupatorium ×cordigerum |
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Phenology | Flowering Jul–Aug. | |||||||||
Habitat | Margins of woods, moist areas | |||||||||
Elevation | 10–100+ m (0–300+ ft) | |||||||||
Distribution |
AL; AR; CT; DC; DE; FL; GA; IN; KY; LA; MA; MD; MO; MS; NC; NH; NJ; NY; OH; OK; PA; RI; SC; TN; TX; VA; WV
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AR; MS; NC; NJ; SC; VA |
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Discussion | 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.) |
Eupatorium ×cordigerum is an apomictic, polyploid hybrid of E. rotundifolium and E. perfoliatum that occurs in disturbed areas where those two species occur together. It is not uncommonly encountered; it is unclear how long it persists. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 21, p. 472. | FNA vol. 21, p. 467. | ||||||||
Parent taxa | Asteraceae > tribe Eupatorieae > Eupatorium | Asteraceae > tribe Eupatorieae > Eupatorium | ||||||||
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Subordinate taxa | ||||||||||
Synonyms | E. rotundifolium var. cordigerum | |||||||||
Name authority | Linnaeus: Sp. Pl. 2: 837. (1753) | (Fernald) Fernald: Rhodora 47: 192. (1945) | ||||||||
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