Land's Edge

The damage done when you discard a land only applies to lands which are discarded by choice using the Land's Edge ability. It does not work on forced discards of any type.

This has the supertype world. When a world permanent enters, any world permanents that were already on the battlefield are put into their owners' graveyards. This is a state-based action called the "world rule." The new world permanent stays on the battlefield. If two world permanents enter at the same time, they're both put into their owners' graveyards.