There are several types of androecium based on how the stamens and filaments are. These types are polyandrous, monadelphous, and diadelphous. Polyandrous is that type of androecium when it has free stamens and they're not united. In the case of a  monadelphous androecium, a group of stamens is not free but is united by their filaments while the anther is free. Similarly in diadelphous androecium, the filaments are united in two bundles and are not free.