Pollen production, flowering and insect visits on Euphorbia cyparissias L. and Euphorbia virgultosa Klok

This study investigated the morphological features, flower biology, pollen output and insects which foraged on Euphorbia cyparissias L. and Euphorbia virgultosa Klok. The observations were made between 2002 and 2006 on ruderal plots in Lublin, south eastern Poland. Both species formed inflorescences of the pseudantium type, known as cyathia. The number of inflorescences was 117.06 per shoot for E. cyparissias and 84.72 for E. virgultosa. The opening of spathe in the successive cyathia occurred almost simultaneously in both species, as early as at 6.00 h with the peak between 7.00 and 8.00 h. All cyathia of E. cyparissias are hermaphroditic. In the case of E. virgultosa, the bisexual cyathia on the shoots accounted for 58.3 %. Hermaphroditic cyathia are protogynous. Dichogamy in Euphorbia virgultosa is strengthened through the occurrence of exclusively male flowers in part of the cyathia. The mean number of anthers per cyathium in E. cyparissias and E. virgultosa, was 17.22 and 14.22, respectively. The small stamens of E. cyparissias yielded a mean of 0.38 mg of pollen per 100 anthers while the larger stamens of E. virgultosa yielded 0.51mg per 100 anthers. The weight of pollen per plant averaged 2.64 mg in E. virgultosa and 3.68 mg in E. cyparissias. Several hymenopteran species (Apis mellifera L. and solitary bees) visit E. cyparissias flowers. Additionally, Bombus spp. forages on E. virgultosa. Among the pollinators of both plants taxa, Diptera were present. Over the five-year period of observation, the density of species studied per square unit varied, but the plants renew each year. The associations with E. cyparissias and E. virgultosa are not subjected to rapid succession. Hence, the studied species should be considered as an important component of the food chain for Apoidea and Diptera.