Eutrochium fistulosum
hollow joe-pye weed, trumpetweed
usually purple throughout, sometimes greenish or purple-spotted, hollow proximally, usually glabrous proximally (rarely pubescent toward bases when young), ± glandular-puberulent distally and among heads (glaucous throughout, at least when fresh).
mostly in 4s–6s(–7s);
petioles (5–)10–30(–50) mm, glabrous;
blades pinnately veined, narrowly to broadly lanceolate, mostly (8–)12–25(–28) × (1.5–)2–6(–9) cm, bases gradually tapered, margins finely serrate (teeth rounded, blunt), abaxial faces sparingly and minutely ± scabrellous to glabrate, adaxial faces glabrous or sparingly puberulent.
often purplish, 6.5–9 × 2.5–5 mm.
(4–)5–7;
corollas usually pale pinkish or purplish, 4.5–6 mm.
glabrous or outer with hairs on midveins.
in convex to rounded (dome-shaped), compound corymbiform arrays (ultimately broadly cylindric).
3–4.5 mm.
= 20.
Eutrochium fistulosum
In the field, Eutrochium fistulosum is the most distinct species of the genus; herbarium specimens do not always document the distinguishing characteristics: heights commonly surpassing 2 m, proximal stem diameters usually 2 cm or greater, stems strongly glaucous (mostly hollow, sometimes distally hollow), leaves commonly 6 or 7 per node, arrays of heads commonly 30 × 22 cm.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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