Allergen Of The Month--Western Dock.
Published 2014 · Medicine
The genus Rumex contains around 200 species of temperate climate weeds widely distributed throughout the northern hemisphere.1 About two dozen species are found in North America: evenly divided between native and introduced.2 Western dock, Rumex occidentalis (synonym R. aquaticus) is native to North America but is also found throughout Europe. It is found throughout most of Canada, and thewestern and northeastern United States. R. occidentalis prefers moist to wet meadows, stream-banks, shorelines, tide-flats and beaches, in elevations up to 3000 m.2e6 The leaves of docks are generally edible, though bitter due to tannins and oxalates. When grazed on in excess, docks may result in livestock loss, althoughpoisoninghasnotbeenreportedwithhumans.7Dockroots havebeenusedbyChippewa Indians inpoultices for itchingandskin eruptions.8 Several Rumex extracts show cancer inhibitory activity.9 Western dock is an erect perennial with a stout taproot and single red-tinted stem that is un-branched below the inflorescence, and 0.5-2 m tall.5,10 Basal leaves are numerous, leathery, heartto lance-shaped with curly edges. Flowers are pink or green in dense clusters. Rumex species are all wind-pollinated, producing abundant airborne pollen, which may approach that seen with grasses.2,11 Sheep sorrel, R. acetosella, may produce 30,00 grains in one stamen, 180,000 in one flower, and 400 million grains from a single plant.12 Anthesis ismost intense from late April throughMay, persisting into the summer in the U.S., and slightly later in midEurope.2,13 In California and southern Florida, Rumex species may pollinate all year long.2 The impact of Rumex species in causing allergic rhinitis is probably greater than appreciated, but its importance is underestimated because of overlap with the grass pollination season.2 Solomon found numerous symptomatic patients who responded to Rumex skin tests and nasal challenges.14 Polygonaceae is monophyletic, and within the superorder Caryophyllanae, containing Polygonales and Caryophyllales.1 This taxonomy would suggest some reactivity between Rumex species and Chenopod-Amaranth weeds of the family Amaranthaceae. This is undetermined, and cross-reactivity data is limited to preliminary data on Rumex acetosella.14,15 No Rumex allergens have been characterized. Rumexpollengrainsarespheroid,22-34mmindiameter.Thegrains are tetracolporate or stephanocolporate, with long, thin, intruding furrowsofvarying lengths,withasmall, ellipsoidpore (1-3x3-6mm)in the center. The pores aremore apparentwith grainsfixed in glycerine jelly.16 The walls are tectate, with densely spaced columellae, about 1.5 mm thick. Surface is reticulate with thick muri and small luminae. The cytoplasm is densely packed with starch granules.16,17 Text and Photography: Richard W. Weber, M.D.