Desolate Plains

Pay 1 Life: Add {w} to your mana pool. Use this
ability only once per turn, only on your turn.
Pay XX Life: Add {w} to your mana pool. X is
equal to the number of mana produced by this
land so far this turn. Use this only if this land
Has already produced mana this turn.
Desolate Plains does not tap for mana. Do not
untap Desolate Plains during your untap step.