Eupatorium semiserratum
Eupatorium pilosum
smallflower eupatorium, smallflower thoroughwort
ragged thoroughwort, rough boneset
(from short rhizomes) single, densely branched distally, puberulent throughout.
(from short rhizomes) single, sparsely branched distally, densely puberulent to pilose throughout.
usually opposite (distal sometimes alternate, lateral buds dormant or producing 1 pair of leaves); simple, sessile or subsessile;
blades ± 3-nerved distal to bases, elliptic to lance-elliptic, (30–)50–70 × 5–25 mm (lengths mostly 2–5 times widths), bases narrowly cuneate, margins usually serrate, apices acute, faces puberulent or villous, densely gland-dotted.
usually opposite (distal sometimes alternate); simple, sessile or subsessile;
blades ± 3-nerved (distal to bases), elliptic, lanceolate, or lance-ovate, 30–90 × 20–45 mm (lengths mostly 2–2.5 times widths), bases rounded to rounded-cuneate, margins unevenly serrate, apices acute to attenuate, faces puberulent, gland-dotted.
5;
corollas 2.5–3 mm.
5;
corollas 3.5–4 mm.
7–10 in 2–3 series, elliptic, 1–3 × 0.5–1 mm, apices rounded to acute (not mucronate), abaxial faces puberulent, gland-dotted.
7–10 in 2–3 series, oblong to lance-oblong, 2–7 × 1–1.5 mm, apices (sometimes whitish) acuminate to acute, mucronate, abaxial faces puberulent, gland-dotted.
in corymbiform arrays.
in corymbiform arrays.
1.5–2 mm;
pappi of 30–40 bristles 2.5–3 mm.
3–4 mm;
pappi of 30–50 bristles 4–5 mm.
= 20.
= 20, 30, 40.
Eupatorium semiserratum
Eupatorium pilosum
Eupatorium semiserratum has been included within E. glaucescens (E. cuneifolium); it is distinguished by its consistently smaller heads and stems that branch only within the capitulescences. It differs from the similar and sometimes sympatric E. lancifolium by its smaller heads, leaves 3-nerved distal to bases (rather than at bases), as well as preference for wetter habitats. It has been proposed that E. rotundifolium var. scabridum (E. pubescens) represents hybrids between E. semiserratum and E. rotundifolium; it also apparently hybridizes with E. hyssopifolium.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Eupatorium pilosum has been most commonly treated as a variety of E. rotundifolium; it is distinct morphologically by its leaves, which are narrower and 3-nerved distal to bases, rather than 3-nerved from bases. Distal leaves of E. pilosum tend to differ from the proximal by being alternate with entire margins.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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