They're in the Osmosis rules text. Basically a Joker can stand in for any card but has no rank until a card in a lower suit relies on it. You can replace a Joker with the card it stands for, but when you do that you have to move it down into the first row where that rank is still needed, or remove it from play when it's in the bottom row.
I don't have the stats to prove this, but it will probably extend play by at least one round and possibly two or more.