giant sumpweed

not listed

N5? - Secure

SNR - Unranked

not listed

FAC - Facultative

FAC - Facultative

FAC - Facultative

Giant sumpweed is a 18″ to 72″ tall, erect, annual forb that rises from a taproot.

The stems are erect or ascending, finely ridged or grooved, and grayish-green. They are usually unbranched but sometimes have straight, upright branches. They are hairless near the base and are sparsely to moderately covered with fine curved or curled curled hairs above the base.

The leaves are mostly opposite, though the uppermost are sometimes alternate. Lower leaves are long-stalked, the stalks up to 2¾″ long or longer stalks. Upper leaves are short-stalked, the stalks up to ⅜″ long or longer. The leaf blades are egg-shaped, often very broadly egg-shaped, 2⅜″ to 4¾″ long or longer, and 1″ to 5⅞″ wide. They are angled or tapered at the base and tapered to a sharp point at the tip. The lower leaves are sometimes shallowly 3-lobed. There are 3 main veins. The upper surface is slightly rough with a sparse to moderate covering of straight, stiff, sharp, appressed hairs. The lower surface is paler and silky with a moderate to dense covering of long, soft, somewhat appressed hairs. The margins are coarsely toothed, often double toothed, with sharp, forward-pointing teeth.

The inflorescence is a branched array (panicle) with numerous small flower heads at the end of the stems and branches and also rising from the upper leaf axils.

The individual flower heads droop at the end of a 3 ⁄16″ to ¼″ long or longer stalk. The whorl of bracts at the base of the flower head (involucre) is 1 ⁄16″ to ⅛″ long. The disk is composed of 8 to 20, usually no more than 10, male (staminate) florets in the center and usually 5 female (pistillate) florets around the margin.

The staminate florets have stamens with the filaments fused into a tube and the anthers free but closely arranged in a ring. The corolla is about 1 ⁄16″ long and white to pale yellow.

The pistillate florets have stamens with the filaments into a tube and the anthers free but closely arranged in a ring. The corolla is sometimes absent. When present it is about 1 ⁄64″ long and whitish.

The fruit is an egg-shaped, dark brown to nearly black, 1 ⁄16″ to ⅛″ long achene with a tuft of hairs attached to one end.

18″ to 72″

White to pale yellow

Moist. Shores, disturbed sites.

August to October

Sources

2, 3, 4, 5, 7, 28.

This genus and five other genera were recently (2000) separated from the genus Iva. The new genus Cyclachaena contains only one species, Cyclachaena xanthiifolia. Many sources continue to use the former name, Iva xanthiifolia.

In 2009 the spelling of the species level name was “corrected” from xanthifolia to xanthiifolia.

Plant

Inflorescence

Flower Heads

Leaves