Urtica membranacea and the importance of its separation from the rest of the Urticaceae in aeropalynological studies carried out in the Mediterranean region

Abstract

The aerobiological behaviour of the Urtica urens and Urtica membranacea pollen types was analysed in Badajoz and Mérida (SW Spain) in order to determine the importance of separating them in studies carried out within the area of distribution of Urtica membranacea. In the two study sites, Urticaceae pollen concentrations in the atmosphere ranged between 1055.7 and 2866.2. This puts them in an intermediate position among the locations that have been studied in the Iberian Peninsula. Annually, more than 25% of these amounts corresponded to Urtica membranacea pollen. The Urtica urens pollen type was present in the atmosphere almost all year round, although its maximum concentrations occurred in February. Its daily concentrations correlated negatively with temperature, wind speed, and westerly winds, and positively with relative humidity, calm periods, and easterly winds. The annual index seemed to be negatively influenced by winter rainfall, and positively by winter maximum temperatures. The hourly pattern of pollination showed low concentrations throughout the night, and a single peak between noon and early afternoon. Urtica membranacea pollen was present in the atmosphere from February to May, and its maximum concentrations occurred between March and April. While its daily variations did not seem to be consistently influenced by any of the meteorological factors analysed, the annual indices positively correlated with the minimum temperatures, which also affected the beginning and the duration of the principal pollination period. The hourly pattern of pollination showed that its presence was not restricted to the early afternoon, but that, on occasions, its maximum concentration occurred at the end of the day (up to midnight).