The filament of a flower is one of the male reproductive parts of the plant. When a flower opens, the filaments can be seen inside, thrusting up like stems within the flower itself. A filament is topped by the anther. Together the anther and filament make up the flower's stamen.
Plants vary in the number of stamens and therefore filaments. Some species may only have one stamen, others have several dozen.
Filaments are short as the flower develops. When it opens, they lengthen.
Filaments exist to carry nutrients to the anther, where pollen develops. After the flower opens, the lengthening filaments facilitate access to the anthers and pollinating agents like bees.
In plants with multiple filaments, they are arranged in a circle around the inside center of the flower.
Some plants have stamens that are fused together. The hibiscus is one of these.
Anthers can top the filament in three ways. Sometimes the filament attaches to the anther at its base, but sometimes it is attached between two lobes of the anther, running up its back. The filament might also plug into one spot on the back of the anther.