Eupatorium hyssopifolium L.

Hyssop-Leaved Thoroughwort

Eupatorium hyssopifolium plant

Family - Asteraceae

Stems - Erect, to 1 m, moderately to densely short-hairy.

Leaves - Mostly in whorls of 3-4, sessile, linear to oblong-elliptic, entire or with a few shallow teeth, often revolute, variously pubescent, gland-dotted, with single midvein. Nodes usually with fascicles of axillary leaves.

Eupatorium hyssopifolium node
Node of stem showing fascicled smaller leaves.

Inflorescence - Terminal panicles, +/- flat-topped.

Involucre - Narrowly cup-shaped, 4-6 mm long. Bracts with blunt tips.

Eupatorium hyssopifolium involucreInvolucres.

Ray flowers - Absent.

Disk flowers - Disk florets 5 per head, with corollas 3.5-4.0 mm, often glandular, white. Styles exserted at anthesis.

Eupatorium hyssopifolium flowers

Flowering - August - November.

Habitat - Dry open ground surrounding upland sinkhole ponds.

Origin - Native to U.S.

Other info. - This showy species is rare in Missouri, being found in only a few counties in the eastern Ozark division. This species is common in the Coastal Plain of the eastern U.S. and has been slowly extending its range northward. The Missouri plants are considered to be var. calcaratum Fernald & B.G. Schub. Other infraspecific forms are recognized by many authors, however, there is significant intergradation. The species can hybridize with other members of the Eupatorium genus, giving apparently fertile forms with intermediate morphology.
Another rare species, E. cuneifolium Willd. is similar but this plant lacks the fascicles of small leaves in its nodes and has broader leaves. E. hyssopifolium also has bigger, brighter flowers.

Photographs taken in the Croatan National Forest, NC., 10-20-02.