The uppermost part of the leaf is flared into a lid (the operculum), which prevents excess rain from entering the pitcher and diluting the digestive secretions within.

The opening of the pitcher tube is retroflexed into a 'nectar roll' or peristome, whose surface is studded with nectar-secreting glands.

Insects losing their footing on this surface plummet to the bottom of the tube, where a combination of digestive fluid, wetting agents and inward-pointing hairs prevent their escape.

Some large insects (such as wasps) have been reported to escape from the pitchers on occasion, by chewing their way out through the wall of the tube.

Currently, there are six subspecies: These placings are somewhat disputed, however, as each could arguably be its own species due to differences in pitcher morphology.