Eutrochium fistulosum (Barratt) E.E. Lamont

Hollow-Stemmed Joe-Pye Weed

Eutrochium fistulosum plant

Family - Asteraceae

Stems - To +2m tall, erect, simple, herbaceous, hollow, solid purple to purplish-green with purple mottling, glabrous, typically glaucous, from fibrous roots.

Eutrochium fistulosum stemStem.

Eutrochium fistulosum stem2Hollow stem.

Leaves - In whorls of 4 to 6, petiolate. Petiole to +2cm long, glabrous. Blade to +25cm long, +8cm broad, elliptic to elliptic lanceolate, serrate, acuminate, pubescent below. Teeth of margins with minute prickle tip caused by vascular tissue extending beyond leaf tissue.

Eutrochium fistulosum leavesLeaf whorls.

Eutrochium fistulosum leavesLeaves.

Inflorescence - Flower heads in terminal paniculate cyme to +30cm tall (long), +/-20cm broad. Branches of inflorescence tomentoulose, reddish-purple. Flower heads with 5-6 flowers.

Involucre - 9mm long(tall), 2.5mm in diameter, greenish near base fading to pinkish-purple above. Phyllaries imbricate. Outermost phyllaries tomentoulose. Inner phyllaries mostly glabrous and with ciliolate margins.

Eutrochium fistulosum involucreInvolucre.

Ray flowers - Absent.

Disk flowers - Flowers +/-5 per head. Corolla tube to 3.1mm long, 5-lobed, pink to purplish, glabrous. Lobes acute, .9mm long, glabrous. Stamens 5, adnate about 1/2 way up corolla tube, alternating with corolla lobes. Filaments pinkish, glabrous. Anthers pinkish-purple, 1.1mm long. Style bifurcate. Stigmas to 3.5mm long, well exserted. Achenes green in flower, 3mm long.

Eutrochium fistulosum floretsDisk florets.

Eutrochium fistulosum floretsDisk florets.

Flowering - July - September.

Habitat - Moist ground, wet meadows, cultivated.

Origin - Native to 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).


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