muttly13: Cover is two things in the game really. One, anything that blocks line of sight for a direct fire weapon. For example, a bolter cannot fire at a target through a wall. Two, a percentage drop to hit a target in "cover". In the case of your palm tree, it would not block bolter fire from being exchanged but it will make it harder to hit.

Item two is what makes flamers a lot more useful then they appear. And that they somewhat ignore armor, but that doesnt have a lot of impact until you get to the higher difficulties where Chaos Marines can actually survive a round or two of fire.