Weeping willow pollen (Salix babylonica), coloured scanning electron micrograph (SEM). The willow (and poplar) family, Saliaceae, is characterized by having their flowers in catkins, the staminate (male) blossoms are on distinct trees from the pistillate (female) trees. Insect pollination occurs during the months of May through August. The weeping willow belongs to the group known as crack willows, from the brittleness of their twigs at the joints. Magnification: x260 when shortest axis printed at 25 millimetres.