If a creature starts and ends its turn in the spell area, does it take the automatic 2d6 damage while also getting attacked (potentially taking another 2d6 damage) if it moves through it? If a creature doesn't move at all in or around the spell area, does it get attacked?
Would any of this damage be considered continuous damage for the purposes of concentration?
If you are taking continuous damage, such as from an acid arrow or by standing in a lake of lava, half the damage is considered to take place while you are casting a spell. You must make a concentration check with a DC equal to 10 + 1/2 the damage that the continuous source last dealt + the level of the spell you’re casting. If the last damage dealt was the last damage that the effect could deal, then the damage is over and does not distract you.
If you are ending your turn in a location part of the Thorny Entanglement, you are in a state where the damage is assured to continue, as per the "standing in lava" example. So you must make a concentration check for injury.
Note that if you are also entangled as per the spell's other functions, you make two separate concentration checks to cast the spell. If either fails, so too does the spell.
Ok, this never got answered, so I'm bumping and adding a clear example to make sure that I am using Thorny entanglement right;
How I think it works:
Jim is walking along one day when someone casts Thorny Entanglement centered on him (turn 0) - Jim must make an immediate save vs Entanglement (Jim fails)
Next, It is Jim's turn (turn 1). Jim wants to get out of the Thorny Entanglement, so he makes a strength check as a move action (Jim Succeeds) Presumably getting free counts as moving, so he draw an attack (it hits and does 2d6 damage). He then moves (30' normal move, reduced to 15' by the difficult terrain: he can't get out of the area) and ends his turn. Jim must save again vs Entanglement, and takes another 2d6 in damage due to ending his turn in the area (for a total of 4d6 this turn)...
Wonderful, wonderful unclear English.
I see the two ways of taking damage as the same attack, the difference is that when you are within the area of effect the damage is automatic, while it requires a to hit if you are within 15' of the area of effect but not within it.
I see perfectly how it can be read both ways, but generally, there is no double-dipping of the same effect in Pathfinder.
The spell has two damage triggers:
Any creature that moves within 15 feet of the spell’s area is attacked once on its turn by the animated plants.
A creature that enters the spell’s area or ends its turn there automatically takes 2d6 points of piercing damage.
The former occurs during your turn if you move. The latter occurs if you exist in the range. You can get hit twice.
Casting is not moving, so does not trigger the former. If the caster starts and ends in the AoE, then they take continuous damage. Likewise, escaping is not moving so does not trigger damage.