One-note-at-a-time music = monophony, although most harmoniums come with drone stops & many with couplers, the music remains essentially monophonic in a highly evolved melismatic tradition. On the floor? I've seen them played in all positions - even on shoulder staps by children busking on trains:

http://www.youtube.com/watch?v=MnZ9GbWqMrg

Note the use of chords too.