Flora of North America species comparison

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Eupatorium hyssopifolium

hyssop-leaf boneset, hyssop-leaf thoroughwort
Habit Perennials, 50–100+ cm.
Stems

(from short caudices or rhizomes) single, sparsely branched distally, pubescent throughout.
Leaves

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).
Florets

5;

corollas 3–3.5 mm.
Phyllaries

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).
Heads

in corymbiform arrays.
Cypselae

2–3 mm;

pappi of 20–30 bristles 3.5–4 mm.

Eupatorium hyssopifolium
Distribution
from FNA
AL; AR; CT; DE; FL; GA; IL; KY; LA; MA; MD; MO; MS; NC; NJ; NY; OH; PA; RI; SC; TN; TX; VA; WI; WV
[WildflowerSearch map]
[BONAP county map]
Discussion

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.)
Key
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
Source FNA vol. 21, p. 468.
Parent taxa Asteraceae > tribe Eupatorieae > Eupatorium
Sibling taxa
E. album, E. altissimum, E. anomalum, E. cannabinum, E. capillifolium, E. compositifolium, E. godfreyanum, E. lancifolium, E. leptophyllum, E. leucolepis, E. linearifolium, E. mikanioides, E. mohrii, E. perfoliatum, E. petaloideum, E. pilosum, E. resinosum, E. rotundifolium, E. semiserratum, E. serotinum, E. sessilifolium, E. ×cordigerum, E. ×pinnatifidum
Subordinate taxa
E. hyssopifolium var. hyssopifolium, E. hyssopifolium var. laciniatum
Name authority Linnaeus: Sp. Pl. 2: 836. (1753)
Web links 
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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