google both, select images, trawl through till you find one showing leaves.

Are you wanting an exact description or just wanting to tell the difference? Both have different varieties and leaf shapes vary so it depends which one you are looking for.

I don't know which varieties grow in the US but in this country the scabious leaves or leaflets tend to be narrow and pointed, while the malva leaves are either broader, or ferny and finely divided in the case of malva moschata.
Malva sylvestris leaves are roughly the same shape as Maple. If none of these match what you are looking for try Althaea officinalis or neglecta.