A canasta is a meld of at least seven cards, whether natural or mixed. A natural canasta is one that comprises only cards of the same rank. A mixed canasta (or dirty canasta) is one that comprises both natural and wild cards. Once a canasta is assembled, the cards are squared up, and one of the natural cards forming it is placed on top - a red one to indicate a natural canasta or a black one to indicate a mixed canasta.