Nepenthes ampullaria : Structure and Function

Nepenthes ampullaria has one of the most unique shapes of all recorded pitcher plants. While most pitcher plants are known for tall, narrow, and individual pitchers, N. ampullaria's pitchers are unusually short and squat and grow in clusters. This difference is owed to the fact that N. ampullaria, unlike other pitcher plants, feeds off decaying leaves (detritivore) instead of animals (carnivore). The pitchers' squat shape and their growth in grounded clusters are adaptations that maximize the plant's surface area and allow the pitchers to catch more falling leaves and leaf debris.

In its switch from carnivory to detritivory, N. ampullaria has developed a number of adaptations unique from other pitcher plants. Most notably, they lack lunate cells and waxy zones, a majority of nectar glands, and a "lid" leaf that covers the mouth of the pitcher. Lunate cells and waxy zones refer to the structures that line the inside of most pitcher plants whose slipperiness cause insects to fall into the pitchers and become unable to climb out. Nectar glands attract insects to pitchers, while lids help prevent insects from escaping once inside. Since N. ampullaria feeds on falling leaves instead of insects, nectar glands, lunate cells, and waxy zones became irrelevant and lids stopped leaves from falling in the pitchers, so these traits have been subsequently lost. In fact, the digestive fluid that fills its pitchers is not even harmful to numerous animals, serving only to break down leaf debris.

N. ampullaria prefer to stick close to the ground to best catch falling leaves. Although their shoots can grow up to 50 ft. long, a vast majority of the pitchers tend to grow along the ground, and any pitchers that grow higher up are considerably smaller. The pitchers are, interestingly enough, actually classified as modified leaves. The grounded pitchers are usually less than 4 in. tall and less than 3 in. in diameter. The colors of the pitchers can also vary widely, ranging from bright green to spotted red to even a deep black.

Nepenthes ampullaria : Evolutionary Relationships

The only genus in the family Nepenthaceae is Nepenthes, the genus of tropical pitcher plants. Of the ~170 species that make up Nepenthes, N. ampullaria is the only one that is a known detritivore, which makes it all the more unique. The shared ancestor of the tropical pitcher plants was what passed carnivory on to all its descendents in Nepenthes, so it's not that N. ampullaria did not evolve to be a carnivore, but rather that it evolved past being a carnivore.

N. ampullaria's switch in its diet from insects to leaf debris can likely be connected to its habitat: wet, dark tropical forests. These tropical forests feature highly dense tree canopies with abundant plant growth at lower layers as well, which provide a fantastic source of falling leaves from both trees and taller ground plants. Since the structure of pitcher plants was most suited to take advantage of this abundant food source, N. ampullaria simply adapted its structure, seen in its loss of nectar glands, lunate cells, waxy zones, and lids, to prioritize these leaves instead.

One of the evolutionary families Nepenthes is most closely related to is Droseraceae, otherwise known as the sundews. Droseraceae, interestingly enough, is one of the largest families of carnivorous plants and is often known for its secretion of a sticky, attractive mucus and curling leaves that trap curious insects. This family also includes one of the most famous carnivorous plant species: the Venus flytrap. 

Nepenthes ampullaria : Ecology

Nepenthes ampullaria can be widely found across Southeast Asia, particularly Indonesia, the Malay Peninsula, Singapore, and New Guinea, and mostly grows on the floor of moist and dark forests.

N. ampullaria plays host to 59 known species that live in its pitchers, mostly inside the digestive fluids. These species primarily consist of fly and midge larvae, mites, and ants. Mosquito larvae in particular are crucial to the plant's survival due to the larvae's role in breaking down leaf detritus, which they then excrete as nitrogen for the plant to feed off of. Quite a few other interesting species have special relationships with N. ampullaria as well. For example, the Matang narrow-mouthed frog, one of the smallest Afro-Eurasian frogs documented (less than half an inch long), spends most of its life in the pitchers. Geosesarma malayamum are small crabs that often enter the pitchers to eat the insects inside. N. ampullaria also host a type of crab spider, Misumenops nepenthicola, which don't use webs to catch prey but wait beside the pitchers to ambush insects.