Eupatorium album
Eupatorium semiserratum
white thoroughwort
smallflower eupatorium, smallflower thoroughwort
(from short caudices or stout rhizomes) single, sparsely branched distally, pubescent throughout.
(from short rhizomes) single, densely branched distally, puberulent throughout.
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); 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.
(4–)5;
corollas 4–4.5 mm.
5;
corollas 2.5–3 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.
7–10 in 2–3 series, elliptic, 1–3 × 0.5–1 mm, apices rounded to acute (not mucronate), 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.
1.5–2 mm;
pappi of 30–40 bristles 2.5–3 mm.
= 20.
Eupatorium album
Eupatorium semiserratum
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.)
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.)
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 |
Go Botany
LA Plants
MD Biodiversity
WildflowerSearch
iNaturalist
USDA Plants Database
