This mass of writhing vines and leaves looks like a large patch of seaweed. Several long fronds protrude from the center of it.
Strangle weed is an ambush predator, relying on its similarity to seaweed to remain inconspicuous until prey wanders near, whereupon it lashes out with its fronds, attempting to grapple its foes, then pull them beneath the water and crush them.
Since a strangle weed looks like normal seaweed when at rest, it takes a DC 20 Perception check to notice it before it attacks. Anyone with ranks in Survival or Knowledge (nature) can use one of those skills instead of Perception to notice the plant.
Strangle weed attacks with fronds that can extend up to 20 feet from its central mass. Each strangle weed has 3-12 fronds. A strangle weed attacks with these fronds as a slam attack; although it can make only one attack per round, if it grapples a foe it is not denied its Dexterity bonus against non-grappled foes and can still make attacks of opportunity if it has any free fronds. Once a foe is grappled, the strangle weed can attempt to latch on 1-4 additional fronds each round as a standard action by means of a separate grapple check. Additional fronds attached to a foe do not do increased damage, but they do add a cumulative +2 bonus to the strangle weed's CMB on subsequent grapple checks against that foe. To free itself, the foe must succeed on a grapple check against every frond grappling it.