While S. montanum minimum is really tiny, S. pumilum hepworth is almost as small.
I need to take a new picture of it since it's propagated like mad, but it's so hot out.
S. montanum minimum has also propagated like crazy over the years, and yet it still doesn't take up much real estate.
S. Speciosum is a must have for those who like the minis. Mine is so gorgeous right now.