In Nepenthes pitchers, the collar-like rim around the mouth is called the peristome.
The peristome is often brightly coloured, ridged, and slippery. It surrounds the pitcher’s entrance and helps lure or destabilise prey. In wet conditions, a thin film of water can make the surface especially difficult for insects to grip, causing them to slide into the digestive fluid below.
The peristome is easy to confuse with nearby pitcher structures. The operculum is the lid above the opening, while the tendril is the curling stalk that supports the pitcher. Lamina refers to the leaf blade, not the rim of the trap.
Nepenthes pitchers are modified leaves rather than separate flowers or fruits. The pitcher’s lower interior contains glands that absorb nutrients, while the lid can help limit rain dilution and may bear nectar glands that attract animals.