Hidden among its pink blossom is a camouflaged set of "finger"-like tendrils, that have "spines" or sharp sensitive sensory organs on the back of each of them. It protects itself from predators by retreating into its hard wood-like trunk. It does this by expanding and contracting cells in the trunk's interior. Its roots collect water for the plant, which it can store for periods in an underground reservoir, where its reproductive organs are also located.
Its diet consists primarily of bat-like creatures native to Zeta Reticuli A, small ground-traveling animals and nearby insects. It wrestles the animal into its mouth using its finger-like dendrites.
It is capable of locomotion, and has a rudimentary nervous system. Despite not having a "brain", it is capable of communicating with others of its species through a chirping sound, often to alert danger. It forces air through a voice box inside its digestive tract. They were also known to purr in the presence of someone it felt safe with. (TOS reference: Star Fleet Medical Reference Manual, ST reference: The Worlds of the Federation)
In 2266, a weeper (nicknamed "Beauregard") was kept in the botanical gardens aboard the USS Enterprise, and was studied by Lieutenant Hikaru Sulu. (TOS episode & novelization: The Man Trap; TOS novel: The Captain's Daughter)