I have also been using them as a hazard in Zone Alfa.
In the book the Triffids are tall, thin, mobile carnivorous plants. The main body is a long stem with a spotted flower,. Inside the stem and flower is a long stinger that flicks out to poison its victim, somehow the stinger seems to target the eyes blinding the victim as the poison takes effect. Though not specifically stated (from memory) some humans are more resistant that others. Where the Triffid meets the ground is a "bulb" from which 3 mobile stumps protrude that allow them to walk at slow speeds. Roots also grow from the bulb that suck the fluids from the victim as it rots and they may also pump in an accelerant to speed the decomposition. Sticking out of its bulb are sharp spines that are used for communication.