Helenium amarum (Raf.) H. Rock

Bitterweed

Helenium_amarum_plant.jpg
STATS

Introduced
CC = *
CW = 3
MOC = 52

© SRTurner

Family - Asteraceae/Heliantheae

Habit - Taprooted annual forb.

Stem - Ascending to erect, to 40 cm or more, usually branched, finely ridged, not winged, glabrous or sparsely pubescent with short, antrorse hairs, also moderately to densely dotted with sessile to impressed, yellow glands.

Helenium_amarum_stem.jpg Stem.

© SRTurner

Leaves - Deeply pinnately divided, glabrous but densely dotted with sessile to impressed, yellow glands. Basal and lowermost stem leaves absent or withered at flowering, somewhat smaller than the median stem leaves, the blade outline linear or rarely ovate and then deeply pinnately divided into narrowly linear segments. Median and upper stem leaves 1-8 cm long, linear to narrowly linear, unlobed, the margins entire, tapered at the base, not decurrent along the stem, tapered to a sharply pointed tip.

Helenium_amarum_leaves.jpg Leaves.

© SRTurner

Inflorescences - Solitary heads terminal branch tips, the heads appearing mostly long-stalked.

Helenium_amarum_inflorescence.jpg Inflorescence.

© SRTurner

Heads - Radiate. Involucre 5-9 mm long, 6-12 mm in diameter, saucer-shaped. Involucral bracts 15-21, in 2 unequal to subequal series, usually with a bluntly thickened, sometimes pinkish- or purplish-tinged midnerve, glabrous or the outer surface sparsely pubescent with minute, ascending hairs, both surfaces also densely gland-dotted. Receptacle strongly convex, hemispherical to nearly globose, often slightly enlarging as the fruits mature, naked.

Helenium_amarum_heads.jpg Heads.

© SRTurner

Helenium_amarum_head.jpg Head.

The combination of wedge-shaped ray ligules having lobed tips, along with the globose array of disk florets at the center of the head, is strongly associated with plants in the Helenium genus.

© SRTurner

Helenium_amarum_involucre.jpg Involucre.

© SRTurner

Florets - Ray florets 5-10 in usually 1 series, pistillate, the corolla 5-12 mm long, relatively broad above a slender base, yellow, the tubular portion and the undersurface of the ligule with sparse to moderate, minute, curled hairs and also with moderate to dense, sessile and spherical or somewhat impressed, yellow glands. Disc florets numerous, perfect, the corolla 1.5-3.0 mm long, yellow, glandular, the 5 sharply pointed lobes also glandular on the outer surface. Style branches with the sterile tip slightly expanded and more or less truncate. Pappus of 6-8 scales, 1.0-1.8 mm long, these papery and white or thinner and nearly transparent, lanceolate to narrowly ovate, tapered to a relatively long-awned tip, the margins usually slightly irregular.

Helenium_amarum_florets.jpg Florets.

© SRTurner

Fruits - Achenes 0.7-1.5 mm long, wedge-shaped, with 4 or 5 angles or slender ribs, the surface brown, relatively densely pubescent with ascending, yellowish hairs.

Helenium_amarum_fruits.jpg Fruits.

The pappus is thin and papery, and topped with a long, threadlike awn.

© SRTurner

Flowering - June - November.

Habitat - Roadsides, pastures, forest openings, prairies, railroads, open disturbed areas.

Origin - Native to the southern U.S.

Lookalikes - Broadly, other species in the Helenium genus.

Other info. - This distinctive species is found in Missouri mostly south of the Missouri River. It is relatively uncommon near the center latitude of the state, becoming much more common toward the southern border. In regions near the Bootheel it is a very common roadside weed. In the U.S. its distribution is mostly southern and southeastern. Though considered introduced in Missouri, it is apparently native in nearby Oklahoma and farther south, in Texas and Louisiana.

Helenium amarum is an easily recognized species. In our flora, only plants in the Helenium genus have the peculiarly wedge-shaped ray ligules along with a protuberant, nearly spherical central array of disk florets. Among these, only H. amarum has the deeply divided leaves with threadlike segments. This and other members of the genus contain sesquiterpene lactones which render the plants bitter and toxic. Ingestion causes a condition known as "spewing disease," which is characterized by vomiting, diarrhea, and in severe cases, death. The bitter compounds can also be carried into the milk of cows which have grazed on the plants. It is because of these properties that the species is colloquially known as "bitterweed." Fortunately, it is usually avoided by cattle (but not by sheep), and is in fact an indicator of overgrazed pastures.

Photographs taken at Crowley's Ridge Conservation Area, Stoddard County, MO, 8-14-2009, in Pilot Knob, Iron County, MO, 7-29-2013, at Holly Ridge Conservation Area, Stoddard County, MO, 8-13-2015, and along the Glade Top Trail, Ozark County, MO, 9-23-2017 (SRTurner).