Eupatorium album
Eupatorium hyssopifolium
white thoroughwort
hyssop-leaf boneset, hyssop-leaf thoroughwort
(from short caudices or stout rhizomes) single, sparsely branched distally, pubescent throughout.
(from short caudices or rhizomes) single, sparsely branched distally, pubescent 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 or whorled (distal sometimes alternate, spreading or horizontal); simple, sessile;
blades 3-nerved from bases (laterals sometimes weak), lance-linear, lance-oblong, or linear, 20–60 × 2–15 mm (lengths mostly 6–40 times widths), bases cuneate, margins entire, laciniate-serrate, or serrate, apices acute, faces scabrous (at least abaxial).
(4–)5;
corollas 4–4.5 mm.
5;
corollas 3–3.5 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.
8–10 in 2–3 series, elliptic to oblong, 1.5–5 × 1–1.5 mm, apices obtuse to acute (not mucronate), abaxial faces pubescent throughout (more densely distally).
in corymbiform arrays.
in corymbiform arrays.
2.5–3.5 mm;
pappi of 40–50 bristles 3.5–4.5 mm.
2–3 mm;
pappi of 20–30 bristles 3.5–4 mm.
Eupatorium album
Eupatorium hyssopifolium
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.)
Varieties 2 (2 in the flora).
Eupatorium hyssopifolium includes both diploid and polyploid cytotypes and presents a complex situation taxonomically. The diploids are placed here in var. hyssopifolium, which also includes polyploids and is characterized by relatively narrow leaves. Variety laciniatum has broader leaves and molecular data suggest that it arose through hybridization between var. hyssopifolium and E. serotinum; the name E. torreyanum has been applied to plants of similar morphology, but these are hybrid derivatives of E. serotinum and E. mohrii. It has also been suggested that var. hyssopifolium has hybridized with E. album var. album to form E. saltuense, and with diploids of E. linearifolium to form polyploid populations included here under E. linearifolium. Eupatorium hyssopifolium is characterized by a tendency for the leaves to be whorled, in 3s and 4s, and for axillary buds to produce leaves without expansion of shoots; the combination of whorled leaves and suppressed axillary shoots gives the nodes a somewhat tufted or verticillate appearance.
(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 |
1. Leaves mostly linear, 2–5 mm wide, margins usually entire or obscurely serrulate | var. hyssopifolium |
1. Leaves mostly lance-linear to lanceolate, 5–15 mm wide, margins usually laciniately toothed | var. laciniatum |
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