Flora of North America species comparison

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Eupatorium semiserratum

smallflower eupatorium, smallflower thoroughwort
Habit Perennials, 40–100+ cm.
Stems

(from short rhizomes) single, densely branched distally, puberulent throughout.
Leaves

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.
Florets

5;

corollas 2.5–3 mm.
Phyllaries

7–10 in 2–3 series, elliptic, 1–3 × 0.5–1 mm, apices rounded to acute (not mucronate), abaxial faces puberulent, gland-dotted.
Heads

in corymbiform arrays.
Cypselae

1.5–2 mm;

pappi of 30–40 bristles 2.5–3 mm.
2n

= 20.

Eupatorium semiserratum
Phenology Flowering Aug–Sep.
Habitat Moist to boggy, sandy, peaty soils, margins of pine flatwoods, gum swamps, bayheads, disturbed sites, roadsides
Elevation 10–100+ m (0–300+ ft)
Distribution
from FNA
AL; AR; FL; GA; LA; MS; NC; SC; TN
[WildflowerSearch map]
[BONAP county map]
Discussion

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.)
Source FNA vol. 21, p. 473.
Parent taxa Asteraceae > tribe Eupatorieae > Eupatorium
Sibling taxa
E. album, E. altissimum, E. anomalum, E. cannabinum, E. capillifolium, E. compositifolium, E. godfreyanum, E. hyssopifolium, E. lancifolium, E. leptophyllum, E. leucolepis, E. linearifolium, E. mikanioides, E. mohrii, E. perfoliatum, E. petaloideum, E. pilosum, E. resinosum, E. rotundifolium, E. serotinum, E. sessilifolium, E. ×cordigerum, E. ×pinnatifidum
Synonyms E. cuneifolium var. semiserratum
Name authority de Candolle: in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 177. (1836)
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Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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