78. Helenium L. (sneezeweed)
Plants annual or
perennial herbs. Stems erect or ascending, sometimes from a spreading base,
unbranched or few- to many-branched mostly above the midpoint, with fine
longitudinal ridges and grooves, sometimes appearing winged, glabrous or
variously hairy, sometimes also with small, sessile, spherical, yellow glands.
Leaves alternate and sometimes also basal, sessile (the basal leaves
occasionally with a short, winged petiole), the base extended downward along
the stems as narrow wings of green tissue (except in H. amarum). Leaf
blades linear to elliptic or narrowly ovate, unlobed, shallowly pinnately
lobed, or (in H. amarum) deeply pinnately divided, mostly angled or
tapered at the base, angled or tapered to a sharply or less commonly bluntly
pointed tip, the margins otherwise entire, wavy or toothed, the surfaces
variously glabrous or hairy, also dotted with relatively dense, sessile to
impressed, yellow to yellowish brown glands, smooth or very slightly roughened
to the touch. Inflorescences of solitary heads terminal on the branches or
appearing as loose, open clusters or open, leafy panicles, the heads appearing
mostly long-stalked. Heads radiate (discoid elsewhere). Involucre more or less
saucer-shaped, the bracts in 2(3) unequal to subequal series, those of the
outer series sometimes fused at the base. Involucral bracts 15–21, green with
sometimes thinner, white margins, 1-nerved, spreading to more commonly reflexed
at flowering, linear to narrowly triangular or narrowly lanceolate, the
surfaces and margins glabrous to variously hairy and dotted with relatively
dense, sessile to impressed glands. Receptacle strongly convex (hemispherical
to broadly conical or nearly globose), often slightly enlarging as the fruits
mature, naked. Ray florets 5–21 in usually 1 series (absent elsewhere),
pistillate or sterile, the corolla relatively broad above a slender base,
yellow, occasionally with reddish streaks or reddish-tinged toward the base,
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, not persistent at fruiting. Disc florets 75
to numerous (more than 500), perfect, the corolla 1.5–4.0 mm long, yellow or
reddish brown to dark purple, the tube not expanded at the base (but somewhat
expanded above the base) or persistent at fruiting, glandular, the 4 or 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 5–8
scales, these papery and white or thinner and nearly transparent, lanceolate to
narrowly ovate, tapered to a short- or relatively long-awned or sharply pointed
tip, the margins usually slightly irregular (toothed or fringed elsewhere).
Fruits wedge-shaped to narrowly wedge-shaped in outline, 4–8-angled or ribbed,
the surface moderately to densely pubescent with ascending hairs, at least on
the angles or ribs, often also glandular, brown. About 35 species, North
America to South America, Caribbean Islands.
Species of Helenium
contain helenanolide sesquiterpene lactones, especially helenalin and tenulin,
which render the plants bitter and toxic. Ingestion of significant quantities
causes a condition known as spewing disease, first recognized in cattle grazing
on other species in high-elevation pastures in the western states (Burrows and
Tyrl, 2001). Symptoms include vomiting, diarrhea, and death. The bitter flavor
of tenulin (the main compound in H. amarum) can also flavor milk from
cattle that have grazed on these plants. Because livestock avoid ingesting Helenium
species unless no other food sources are available, the genus (particularly H.
amarum) is an indicator of overgrazed pastures.