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Pollination ecophysiology of Mercurialis annua L. (Euphorbiaceae), an anemophilous species flowering all year round

Lisci, M., Tanda, C., Pacini, E.
Annals of botany 1994 v.74 no.2 pp. 125-135
flowering, dimorphism, gynoecium, pollen, pollen tubes, plant morphology, rain, seasonal variation, temperature, Mercurialis annua, pollination, ultrastructure, Italy
Mercurialis annua L. is a dioecious anemophilous species that flowers all year round in central and southern Italy. The flowers of both sexes are dimorphic: the female flower has a vestigial calyx, the male flower consists only of a calyx that opens at anthesis. The anthers always dehisce after anthesis. The anthesis of male flowers seems to be temperature dependent, whereas anther dehiscence is related to relative humidity. The pollen grains vary in volume according to the season: they are smaller when relative humidity is low and vice versa. They always decrease in volume after anther dehiscence and have the capacity to vary in volume and reach equilibrium with a changing environment. Viability is high, but may drop suddenly during heavy rain or hail that damage the exposed male flowers. The number of pollen grains per stigma varies from 0 to 300, The data is discussed in relation to the type of pollination and environmental characteristics.