There is a check box for each of the following layers: Petals, Stamen, Pistil, Sepals and Receptacle.
Clicking in the check box will create a selection tag, in the Objects Manager, for the applicable item.
Clicking on the appropriate selection tag will then enable you to assign layers, such as materials, to this item, individually.
All Selections enabled and selection tags present in the Objects Manager.
You can also use the selections in xpEmitter to generate particles from specific flower parts.
In this final image, the xpEmitter Emitter Shape is restraining the particle emission to the Stamen, which has been dropped into the Selection field..