Eutrochium fistulosum (Barratt) E.E. Lamont

Hollow-Stemmed Joe-Pye Weed

© DETenaglia

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.

	Stem.
© DETenaglia

	Hollow stem.
© SRTurner

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.

	Leaf whorls.
© SRTurner

	Leaf abaxial.
© SRTurner

	Pressed leaves.
© DETenaglia

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.

	Inflorescence.
© SRTurner

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.

	Involucre.
© SRTurner

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.

	Disk florets.
© SRTurner

	Disk florets.
© SRTurner

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.

The species epithet fistulosum means tubular or hollow, referring to the stems. The large central cavity in the stem is another character for differentiating the plant from E. purpureum, though this must be interpreted cautiously, as stems of other species of Eutrochium can also have hollow regions.

A synonym for this species is Eupatorium fistulosum Barratt.

Photographs taken off Hwy 40 near Knoxville, TN, 8-9-04 (DETenaglia), also at Shaw Nature Reserve, Franklin County, MO, 8-18-2017 (SRTurner).