Rough marshelder

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Code: w16
Latin name: Iva ciliata (Synonym: I. annua)
Source material: Pollen
Family: Asteraceae
Common names: Rough Marshelder, Rough Marsh Elder, Annual Marshelder, Annual Marsh-Elder, Sumpweed

Allergen Exposure

Rough Marshelder is native to Northern America, in particular to Mexico, and to Nebraska and Texas in the USA. Although some species of the genus Iva have been introduced in other parts of the world, most are found in the North American states of Texas, Louisiana, Mississippi, Oklahoma and Nebraska. Rough Marshelder pollen rivals Ragweed pollen in the Mississippi Delta. Related species are found in Canada and Australia.

Rough Marshelder is an annual weed with fibrous roots, and grows up to 2m in height. It usually reaches half this height. It has an odour like Ragweed and can be mistaken for that weed. The stems are erect, branched, and hairy. The leaves are hairy, opposite, simple, and oval in shape with a pointed tip. They grow up to 15cm long and 7cm wide. Each leaf is irregularly toothed.

Flowering occurs from July to October. The flowers are clustered in small heads, each head up to 4mm long. The heads are in cylindrical spikes in a branched inflorescence, from the leaf axils and terminal. The flowers are green to cream in colour. The flower parts are not discernable with the naked eye. The flowers result in fruits that are 2 to 3mm achenes, dark-brown, flattened, and with a somewhat triangular shape.

Species of Iva differ from species of Ambrosia, the Ragweeds, by having only one kind of flower, as opposed to the Ragweeds’ pollen-producing flowers in elongated spikes and pistil-producing flowers in short clusters in the axils of the leaves. Rough Sumpweed differs from other species in the genus by its rough and hairy leaves.

Marshelder grows in marshy areas, such as wet meadows, prairies, fallow fields and roadsides, stream banks and the shores of ponds and lakes.

Allergen Exposure

No allergens from this plant have yet been characterised.

Potential Cross-Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected, as well as to a certain degree among members of the family Asteraceae. (1)

In a study using a fluorescent allergosorbent test, similar antigenic determinants were found between Short and Giant Ragweed, Cocklebur, Lamb's Quarters, Rough Pigweed, Marshelder, and Goldenrod. Cocklebur and Giant Ragweed were highly potent in their ability to competitively bind to Short Ragweed IgE. The other pollens demonstrated lower potency of cross-reacting antigens. (2)

Clinical Experience

IgE mediated reactions

Anecdotal evidence suggests that asthma, allergic rhinitis and allergic conjunctivitis are common following exposure to pollen from Rough Marshelder; however, few specific studies have been reported to date. (3, 4, 5, 6, 7, 8)

Of 1159 patients with asthma and allergic rhinitis attending an allergy clinic in Saudi Arabia who tested positive to one or more inhalants, 23.4% were sensitised to Rough Marshelder. The prevalence of sensitisation to this allergen among the 806 Saudi Arabs was 23.4% and among 241 Western expatriates 20.7%. (3)

In a study in Westchester County in the state of New York of skin prick tests to 48 aeroallergens in100 patients referred for allergic rhinitis, 1% had a positive skin prick test for Marshelder. (9)

In a study in Michigan in the USA, allergens with positive intradermal wheals after negative prick testing included Cocklebur, Rough Marshelder, and Ragweed, all with incidences of 16% to 19%. (6)

Other reactions

Contact with the leaves may result in contact dermatitis.

Compiled by Dr Harris Steinman,


  1. Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09.
  2. Perrick D, Stafford CT, Armstrong E, DuRant RH. Modification of the fluorescent allergosorbent test as an inhibition assay for determination of cross-reactivity among aeroallergens. J Allergy Clin Immunol 1991;87(1 Pt 1):98-103.
  3. Williams O, Speairs R, Boggs HW. Hypersensitivity to marsh elder: difficulties encountered in patch testing. J La State Med Soc 1960 Jun;112:216-9.
  4. Suliaman FA, Holmes WF, Kwick S, Khouri F, Ratard R. Pattern of immediate type hypersensitivity reactions in the Eastern Province, Saudi Arabia. Ann Allergy Asthma Immunol 1997;78(4):415-8.
  5. Stokes JR, Hartel R, Ford LB, Casale TB. Cannabis (hemp) positive skin tests and respiratory symptoms. : Ann Allergy Asthma Immunol 2000;85(3):238-240.
  6. McKay SP, Meslemani D, Stachler RJ, Krouse JH. Intradermal positivity after negative prick testing for inhalants. Otolaryngol Head Neck Surg 2006;135(2):232-235.
  7. Tocker AM. The possible role of Iva ciliata in hay fever therapy. South Med J 1956;49(5):445-52.
  8. Calhoun KH. Patterns of mold sensitivity in the subtropical Gulf Coast. Otolaryngol Head Neck Surg 2004 Mar;130(3):306-11.
  9. Basak P, Arayata R, Brensilver J. Prevalence of specific aeroallergen sensitivity on skin prick test in patients with allergic rhinitis in Westchester County. Internet J Asthma Allergy Immunol 2008;6(2).


As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.