7. Eupatorium purpureum L. (green-stemmed Joe-pye weed)
Eutrochium
purpureum (L.) E.E.
Lamont
Eupatoriadelphus
purpureus (L.) R.M. King
& H. Rob.
Pl. 265 a, b;
Map 1115
Stems 40–200 cm
long (sometimes to 4 m or more in cultivation), solid or rarely becoming hollow
with a slender central cavity (usually toward the base), mostly glabrous below
the inflorescence, dark purple only at the nodes, not or only slightly
glaucous, generally lacking small axillary branches or fascicles of axillary
leaves. Leaves mostly in whorls of 3 or 4(5), the uppermost leaves sometimes
alternate or opposite, the petiole 2–20 mm long. Leaf blades 5–30 cm long, 25–90
mm wide, narrowly ovate to ovate, elliptic-ovate, or triangular-ovate, tapered
at the base, tapered to a sharply pointed tip, the margins sharply toothed, the
upper surface glabrous or sparsely to moderately short-hairy, the undersurface
glabrous to densely short-hairy, also glandular, with 1 main vein.
Inflorescences terminal panicles, often large, broadly to narrowly dome-shaped.
Involucre 6.5–9.0 mm long, slender, the bracts ovate to lanceolate or narrowly
oblong-elliptic, bluntly to sharply pointed at the tip, often 3-nerved, usually
glabrous, usually purplish-tinged to dark purple. Disc florets 4–7(–8).
Corollas 4.5–7.5 mm long, the surface often somewhat glandular, pale pink or
somewhat purplish-tinged. Fruits 3.0–4.5 mm long. 2n=20. July–September.
Scattered nearly
throughout the state but more abundant south of the Missouri River (eastern
U.S. west to Minnesota, Nebraska, and Oklahoma; Canada). Bottomland forests,
mesic upland forests, and banks of streams and rivers; also roadsides.
This is by far
the most common of the three Joe-pye weeds in Missouri. It is sometimes grown
as an ornamental in gardens, and under some conditions it can grow to over 4 m
tall. Native Americans and early European settlers used the three Joe-pye weeds
(especially the rhizomes) medicinally to treat kidney ailments and
inflammations and as a general tonic (Lamont, 1995).
Putative hybrids
between this species and both E. fistulosum and E. maculatum have
been recorded from farther east (Lamont, 1995), but these have not been found
in Missouri to date. Two varieties of E. purpureum have been recognized
by most botanists.