Semaphore Thoroughwort

Perennials, 50–100+ cm. Stems (from short rhizomes, green) single, branched distally, puberulent throughout. Leaves opposite (± vertical); petiolate (petioles 10–30 mm); blades ± 3-nerved distal to bases, deltate to rhombic, 25–80 × 20–60 mm, bases broadly cuneate, margins usually serrate (teeth uneven), sometimes crenate, apices acute, faces glabrate to sparsely puberulent, gland-dotted. Heads in corymbiform arrays. Phyllaries 8–12 in 2–3 series, elliptic to oblong, 1.5–5 × 0.8–1 mm, apices acute to acuminate, abaxial faces puberulent, gland-dotted. Florets 5; corollas 3.5–4 mm. Cypselae 1.2–1.5 mm; pappi of 20–35 bristles 3.5–4.5 mm. 2n = 20.

Eupatorium mikanioides, commonly called semaphore thoroughwort, is a herbaceous perennial plant in the family Asteraceae found only in the US state of Florida.

Like other members of the genus Eupatorium, it produces large numbers of small white flower heads, each head with 5 disc florets but no ray florets. It grows a half meter to one meter tall.

It grows in wet to moist areas, and is salt-tolerant.