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True (Rough) Marsh Elder

WEEDS

GENUS/SPECIES


Iva annua

FAMILY


Asteraceae
(Compositae)

SYNONYMS


Common: Annual Marsh Elder
Botanical: Iva ciliata

DISTRIBUTION


Eastern two-thirds of US

  • New Mexico eastward to Florida
  • Florida northward to Pennsylvania
  • Pennsylvania northwestward to North Dakota
  • North Dakota southward to New Mexico
  • Additional populations in New England

Comments

This native annual weed reaches its best development in the south central part of the US, especially in the Mississippi Delta region. It may exceed 6 feet in height but is usually half this tall. It grows in wet meadows, prairies, and along rivers and ponds. The opposite leaves are pointed, and large ones are about 6 inches long and nearly half that width. The numerous flower clusters, which produce copious pollen, are along spikes found at the top of each branch; both stamens and pistils are present in each of these clusters (unlike Ragweed). Rough marsh elder is rather closely related to the Ragweeds and superficially resembles giant ragweed, but the bracts extending from the flowering spike easily distinguish it. Pollination may extend from May to October, but usually starts in July. Allergenically, it is highly cross-reactive with short ragweed.