7. Eupatorium purpureum L. (green-stemmed Joe-pye weed)
purpureum (L.) E.E.
purpureus (L.) R.M. King
& H. Rob.
Pl. 265 a, b;
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.
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).
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