Interactions between climatic changes and allergenic plants.

Records of the start of some allergenic pollen seasons monitored in Perugia (Central Italy) for the last two decades indicate a trend for the pollen seasons of spring flowering plants to begin earlier. The duration of the pollination of some taxa shows a trend to be shorter while Urticaceae reveal an increase of 20 days for its length over the same period. These trends show a close relationship to an increase in the annual mean air temperature recorded in Perugia in the last years due to, above all, the temperature of February, May, June and August.