Eutrochium fistulosum (Barratt) E.E. Lamont
Hollow-Stemmed Joe-Pye Weed
CC = 8
CW = -5
MOC = 11
Family - Asteraceae/Eupatorieae
Habit - Perennial forb with fibrous roots.
Stems - Erect, to 3 m, simple, herbaceous, hollow with a large central cavity between nodes, solid purple to purplish-green with purple mottling, glabrous, typically glaucous.
Leaves - In whorls of 4 to 7, petiolate. Petiole to 2.5 cm long, glabrous. Blades 5-30 cm long, 1.5-6.0 cm broad, lanceolate to elliptic, sharply toothed, acuminate, glabrous or pubescent below, also glandular, with a single midvein. Teeth of margins with minute prickle tip caused by vascular tissue extending beyond leaf tissue.
Inflorescences - Terminal, dome-shaped panicles of flowering heads to 30 cm tall, 20 cm broad. Branches of inflorescence tomentoulose, reddish-purple. Heads discoid, with 4-7 florets.
Heads - Involucre 6.5-9.0 mm long, slender, the bracts ovate to lanceolate or narrowly oblong-elliptic, rounded or bluntly pointed at the tip, often 3-nerved, often minutely hairy, often somewhat purplish-tinged. Phyllaries imbricate. Outermost phyllaries tomentulose. Inner phyllaries mostly glabrous and with ciliolate margins.
Flowers - Corollas 4.5-7.5 mm long, 5-lobed, the surface often somewhat glandular, pale pink or less commonly somewhat purplish-tinged. Stamens 5, adnate about 1/2 way up corolla tube, alternating with corolla lobes. Filaments pinkish, glabrous. Anthers pinkish-purple, 1.1 mm long. Style bifurcate. Stigmas to 3.5 mm long, well exserted.
Fruits - Achenes 3.0-4.5 mm long.
Flowering - July - September.
Habitat - Forests, swamps, streambanks, moist ground, roadsides. Also cultivated.
Origin - Native to the U.S.
Other info. - This species occurs naturally in only a few counties in Missouri. It is, however, widely cultivated and can be found nearly throughout the state. The brilliant purple stems and large inflorescences make it a desirable plant. This species is often confused with E. purpureum L. but the latter has more greenish stems, which are typically solid, and lighter colored flowers.
Photographs taken off Hwy 40 near Knoxville, TN, 8-9-04 (DETenaglia), also at Shaw Nature Reserve, Franklin County, MO, 8-18-2017 (SRTurner).