Eupatorium rugosum Houtt.

Eupatorium rugaosum plant

Family - Asteraceae

Stems - To +1m tall, erect, herbaceous, single or multiple from base, from many thickened yet fibrous roots, glabrous to densely pubescent (the hairs typically antrorse), simple or branching in especially in inflorescence.

Eupatorium rugaosum stemUpper stem.

Eupatorium rugaosum stemLower stem.

Leaves - Opposite, petiolate, decussate. Petioles to +/-4cm long, with an adaxial groove, pubescent (especially in groove), greenish to purple. Blades ovate, serrate, acute to acuminate, truncate to abruptly acuminate at base, to +/-12cm long, +/-8cm broad, sparse pubescent above and below (mostly on veins), dull deep green adaxially, shiny light green abaxially. Midrib and two basal lateral veins expressed abaxially. Serrations of margin often antrorse strigillose and with a minute light colored tip due to exserted vascular tissue.

Eupatorium rugaosum leaves

Inflorescence - Terminal corymobose arrangement of flower heads. Peduncles densely antrorse pubescent, to 1cm long. Each division of inflorescence subtended by a small bract. Bracts foliaceous near base of inflorescence, reduced upward and becoming thin and linear.

Involucre - To +/-5mm long, 2-4mm in diameter, cylindric. Phyllaries in a single series and only slightly overlapping, linear to linear-oblong, ciliate-margined (especially at the apex), pubescent externally, glabrous internally, slightly cupped, acute, to 5mm long, 1mm broad.

Eupatorium rugaosum involucreInvolucre.

Ray flowers - Absent.

Disk flowers - +/-14 per flower head. Corollas white, 5-lobed, constricted in lower 1/2, expanded in apical 1/2, to 4mm long, glabrous externally and internally. Lobes acute, spreading, pubescent externally, glabrous internally. Stamens 5, adnate at apex of constricted portion of corolla tube. Filaments white, filiform, to .8mm long. Anthers whitish to pale yellow, to 1.2mm long, connate around style, slightly exserted. Style well exserted, bifurcate, translucent-white, glabrous. Stigmas to +2mm long. Pappus a single series of capillary bristles to 3-4mm long. Bristles minutely barbellate (use lens to see). Achene greenish in flower, black in fruit, to +3mm long, 4-5 angled, glabrous to pubescent. Receptacle flat.

Eupatorium rugaosum flowersFlower close-up.

Flowering - July - October.

Habitat - Rich, rocky woods, base of wooded bluffs, rock outcrops, thickets.

Origin - Native to U.S.

Other info. - This species can be found throughout Missouri and is quite common. The plant is variable in its pubescence and a couple different forms are mentioned in Steyermark. I won't go into those here.
This species is very toxic if eaten in quantity as it contains barium sulphate. Cows which graze on the plant produce poisonous milk and this was the cause of death for a number of pioneers in this country.
American Indians used a tea made from the roots to help diarrhea, painful urination, fevers, and kidney stones. The plant was also burned and the smoke used to revive unconscious patients.

Photographs taken at Pilot Mountain State Park, NC., 10-16-02.


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