Annual Marshelder

(Iva annua L.)

Asteraceae (Aster Family)

▲ ▼ mature plants

▲ ▼ inflorescences

Iva annua L., Annual Marshelder, Sumpweed: (Bayer Code: IVAAN; US Code IVAN2)

Native summer annual that grows 1-5 feet tall, with upright stems; branching mainly in upper half of plant; stems, ridged, green to reddish-green or purplish or brown, usually hairless on lower portions and rough-hairy above
Leaves are usually opposite (may be alternate in upper portions of plant), triangular to lanceolate, rough-textured with toothed margins and gland dots; 3 prominent veins in leaf merge at petiole; leaves have moderately long petioles; leave tips often droop slightly in heat of summer; bruised leaves may have a camphor-like or medicinal odor
Small head inflorescences in spikes at stem tips; individual heads are green and release abundant pollen
Small, rough-textured, triangular bracts stick out beyond the individual heads and curve upward
Flowering is from mid-summer to mid-autumn
Prefers full sun and fertile soils with adequate water; found in pastures, prairies, right-of-ways, riparian area; can tolerate roadside salt well
Not usually a serious crop weed problem, although plant releases pollen that can cause allergies similar to ragweed
Plants and seeds were used medicinally and as a food source by native Americans
Appears quite similar to lanceleaf ragweed (Ambrosia bidentata), but can be distinguished by the downward curved bracts in between the little green flowers on lanceleaf ragweed (annual marshelder’s bracts curve upward)

(Updated November 28, 2022)