What is the effective range of Umbrella Leafs?

What is the effective range of Umbrella Leaf plants? Do they protect plants diagonally adjacent to them? If next to a Cob Cannon (2 lawn squares wide), will the Umbrella Leaf protect both "halves" of the Cob Cannon?

Also, do they take damage and need to be repaired/replaced like Wall Nuts?

They don't take damage from normal use, but can still be eaten.

The range of them is themselves plus one square all around them, for a total grid of 3x3 or 9 squares total. If they attack the cob cannon, it will defend whatever square the zombie is falling onto. Put an umbrella on both sides of the cob cannon to fully protect it.