Euthamia leptocephala (Torr. & A. Gray) Greene ex Porter & Britton

Mississippi Valley Flat-Topped Goldenrod

Euthamia leptocephala plant

Family - Asteraceae/Astereae

Habit - Rhizomatous perennial forb.

Stem - Ascending to erect, to 1 m, usually solitary, often branched above the midpoint, glabrous.

Euthamia_leptocephala_stem.jpgStem.

Leaves - Basal and lower leaves absent at flowering. Mid- and upper-stem leaf blades 1-10 cm long, 1-8 mm wide, linear to narrowly lanceolate, sessile, relatively thin in texture, the margins slightly roughened with minute, stout, ascending, stiff hairs, the surfaces glabrous, slightly resinous with sparse or faint, inconspicuous pustular-gland dots, with 1 midvein or more commonly at least the larger leaves often with 3 main veins, the lateral pair usually finer than the midvein.

Euthamia_leptocephala_leaves.jpgStem and leaves.

Euthamia_leptocephala_leaf2.jpgLeaf abaxial.

Inflorescence - Relatively dense, flat-topped panicles, the heads usually in small clusters at the branch tips.

Euthamia_leptocephala_inflorescence.jpgInflorescence.

Heads - Minutely radiate. Involucre 4-6 mm long, roughly cylindrical, not or only slightly resinous, the bracts variously rounded to sharply pointed at the tip.

Euthamia_leptocephala_heads.jpgHeads.

Florets - Ray florets 7-15, pistillate, the corollas 2-3 mm long, the short ligule ascending to somewhat spreading. Disc florets 3-5, perfect, the corolla 2.5-4.0 mm long, the lobes 0.4-0.9 mm long. Pappus of the ray and disc florets similar, of numerous slender, white, finely barbed bristles about as long as the corollas.

Euthamia_leptocephala_florets.jpgFlorets.

Fruits - Fruits 0.5-1.5 mm long, oblong-elliptic to slightly obovate, circular in cross-section or very slightly flattened, faintly 2-4-nerved, the surface moderately pubescent with fine, ascending, white to somewhat silvery hairs, straw-colored to light greenish brown.

Flowering - August - October.

Habitat - Bottomland forests, swamps, sloughs, ditches, often in sandy substrate.

Origin - Native to the U.S.

Lookalikes - Other species in the Euthamia genus; more broadly, goldenrods (Solidago sp.).

Other info. - This species is uncommon in Missouri, known mostly from 8 counties in the Bootheel. In fact, Missouri's Bootheel lies at the extreme north end of the plant's range, which extends southward to the Gulf of Mexico. Although plants in this genus are superficially similar to the goldenrods (Solidago sp.), and were previously classified within that genus, significant differences in head morphology, leaf glands, and genomics support distinct genera for the two groups.

In general, the flat-topped goldenrods (Euthamia sp.) are less common in Missouri than the true goldenrods (Solidago sp.). Plants in these two genera are easily confused. Euthamia is recognized by its dense, flat-topped inflorescences and small, narrow leaves.

Photographs taken at Otter Slough Conservation Area, Stoddard County, MO, 9-11-2019 (SRTurner).



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