Eupatorium linearifolium
Eupatorium serotinum
waxy thoroughwort
late eupatorium, late thoroughwort, lateflowering thoroughwort
(from short caudices) single or multiple, branched at or near bases, pubescent throughout.
(from short caudices) single, sparsely to densely branched distally, pubescent throughout (sometimes reddish to purplish).
usually opposite (distal sometimes alternate);
sessile or subsessile;
blades 3-nerved distal to bases, oblong to lance-oblong, 20–45 × 5–10 mm, bases cuneate, margins entire or serrate (teeth mostly proximal), apices acute, faces finely puberulent, gland-dotted.
opposite; petiolate (petioles 10–25 mm);
blades ± 3-nerved, lanceolate, 20–90+ × 5–40 mm, bases rounded to slightly oblique, margins entire or serrate, apices acute, faces puberulent, gland-dotted.
5;
corollas 3–3.5 mm.
9–15;
corollas 2.5–3 mm.
8–10 in 1–2 series, lanceolate (tapering toward apices), 2–5 × 0.5–1 mm, apices rounded to acute, abaxial faces puberulent, gland-dotted.
8–12 in 1–2 series, elliptic to oblong, 1–3 × 0.5–1 mm, apices slightly rounded to acute, abaxial faces puberulent, gland-dotted.
in corymbiform arrays.
in corymbiform arrays.
2.5–3 mm;
pappi of 30–40 bristles 3–5 mm.
1–1.5 mm;
pappi of 20–30 bristles 2–2.5 mm.
= 20, 30, 40.
= 20.
Eupatorium linearifolium
Eupatorium serotinum
Plants treated here as Eupatorium linearifolium were long treated under the name E. cuneifolium; the latter name was superfluous when published (K. N. Gandhi and R. D. Thomas 1991). Because there appears to be a continuous range of variation between diploids that were referred to by V. I. Sullivan (1972) as E. cuneifolium and the series of putative hybrids (with E. hyssopifolium suggested as the other parent) that she called E. linearifolium, these are combined here. The tendency for the plants to branch at or near the bases is distinctive within Eupatorium.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Eupatorium serotinum has a wide distribution and is often abundant where it occurs. It includes only sexual, diploid populations. It is known to hybridize with E. perfoliatum. An introduction of E. serotinum in southeastern Ontario apparently is local and may not have persisted.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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