SafePlants

Giant Sumpweed (Cyclachaena xanthiifolia)

Giant sumpweed, scientifically known as Cyclachaena xanthiifolia, is a plant belonging to the sunflower family (Asteraceae). It is also commonly known as marsh elder, giant marshelder, horseweed, rag sumpweed, or burweed marshelder.

Taxonomy and Nomenclature

• Scientific Name: Cyclachaena xanthiifolia (Nutt.) Fresen.
• Family: Asteraceae (Sunflower Family) / Compositae
• Kingdom: Not explicitly stated, but as a plant, it belongs to the Plant Kingdom.
• Synonyms: Iva xanthifolia Nutt. (formerly)
• Taxonomic Rank: Species
• Symbol: CYXA2, CYXA
• Group: Dicot

Distribution and Habitat

Giant sumpweed is believed to be native to the Great Plains of North America. It is now found across Canada, the United States, and is newly introduced to regions like Vojvodina, Serbia. It often grows in lowlands and ruderal sites (disturbed areas), including around livestock pens.

Ecological Role

In some regions, such as Vojvodina (Serbia), giant sumpweed is considered a newly introduced, invasive weed.

Morphological Characteristics

• Growth Habit: Annual forb/herb
• Size: Grows up to 1 meter (3ft 3in) in height.
• Flowers: Dense, branching clusters of 1/8-inch green to yellowish disk-shaped flowers.
• Other: Purple stems and petioles have been observed.

Interactions with Other Organisms

• Giant sumpweed is a nut-producing angiosperm (flowering plant).
• It can be a source of airborne pollen, similar to common ragweed and giant ragweed.
• Non-native lady beetles have been observed within patches of goldenrod and giant sumpweed.

Further Information: USDA PLANTS Database, McGregor, R.L., et al. 1977. Atlas of the flora of the Great Plains. Iowa State University, New York Flora Association. 1990. Preliminary vouchered atlas of New York State flora, ed. 1. New York State Museum Institute, Albany, invasive.org