Nepenthes
Nepenthes rafflesiana

from Borneo

 

the species

the species

the hybrids

the ants

The Plant

The terminus "pitcher plants" is used for a number of different carnivorous plants with pitcher-like leaves. But these features have evolved independently in several genera belonging to different families of plants. Nepenthes are the tropical pitcher plants of the Old World. It's the only genus of the Nepenthaceae family. Higher systematic categories and their relations to the New Worlds Pitcher plants (Sarraceniaceae) are still discussed. You can find Nepenthaceae either in Aristolochiales (Magnoliidae) or in it's own Order Nepenthiales (Dilleniidae, as a neighbour to Sarraceniales). There are other suggestions and more interesting questions to solve. At least there is the consensus that they are dicotyledones...
Btw: the name Nepenthes is Old Greek and means "soothing grief"

Nepenthes

pitcher plants
Nepenthes distribution

Distribution

The distribution of the genus Nepenthes (green). Borneo is marked red.

Carnivory is an answer to the lack of nutrients. While plants get their energy from sunlight, air and water, they still need nitrogen and phosphor to grow. Usually these can be found in the soil but in some places they are so rare that it's hard for plants to grow. Some plants have opened up another source: living animals. With sticky leaves, quick closing traps or slippery pitchers they catch insects and digest them to get the precious nutrients.
All Nepenthes grow in extreme habitats poor of nutrients. Peat swamp and mountain rainforests or degraded, eroded areas are typical habitats for pitcher plants. Some are even pioneers growing on pure sand where the tropical forest has been destroyed. When soils are rich they are not strong in concurrence, and other plants are growing faster.

Habitat

Nepenthes rafflesiana growing on white sand where both forest and secondary vegetation have been destroyed by fire and the soil was washed away.

Most Nepenthes grow as lianas, and some can climb more than ten metres up the trees. The tendril of their leaves helps them to get hold on trees and bushes they use as support. Some grow epiphytic, others usually stay as rosettes on the ground.
They usually produce two morphological and sometimes even ecological different types of pitchers. Young plants in the rosette stadium have lower or ground pitchers. Their mouth is looking towards the tendril, and they have 'wings' on the pitcher wall. When the plants begin to climb, they start to produce upper or aerial pitchers. These lack the wings, and the tendril is on the backside of the pitcher. Often these two pitcher types look completely different and are hard to recognise as parts of the same plant.
The leaf morphology is among the strangest found in the kingdom of plants. The pitcher is the lamina or leaf spade; the tendril is the stalk. What looks like the leaf is an extremely enlarged leaf base, the part of the stalk next to the stem.

Morphology

Nepenthes leaf

The leaf anatomy of Nepenthes in comparison to a normal leaf.

Nepenthes are dioecious, that means there are male and female plants. Inflorescences are long raceme- or panicle-like. The flowers have only four leafs (sepals) which are covered with nectar glands. The pollinators of some species seem to be flies and moth, but beetles, bugs and ants are also observed to visit the flowers. The development of the fruit capsule takes about three month. It can contain 500 or more seed. Those are very light and have long wings to be carried by the wind.

A female inflorescence of Nepenthes rafflesiana and two male flowers (top)

The flowers

 
inflorescence

The pitchers are traps to catch small animals. Though not all species use every method, they attract their prey with colour, smell and nectar. Some species are even known to have UV patterns like many flowers have.
The brim of the pitcher, the peristome, produces the highest amount of nectar. When animals try to get it they have to step on the slippery, waxy surface of the peristome and most of them are not able to walk there. They fall into the pitcher and then there is no way back. While the lower half of the pitcher which is filled with the fluid has a glandular wall, the upper half is as slippery and waxy as the peristome. The animals drown in the fluid and are digested by the digestive enzymes.

The pitchers

Pitcher anatomy

The basic structure of Nepenthes pitchers (from "Nepenthes of Borneo" by Charles Clarke, with permission of C. Clarke and C.L. Chan)

While they catch mostly insects there where also found small vertebrates, even rats in bigger pitcher. But these are mere accidents for both sides, and the putrefaction of big prey diminishes the pitchers live span. Carnivorous plants should be rather called insect eating plants.
Some Nepenthes species are highly specialised in their prey. While ants are the most common prey for the lowland species, e.g. N. mirabilis seems to be a real ant specialist. It's extremely attractive for ants, and some pitchers are filled with them. On the other hand, N. albomarginata feeds mostly on termites. How it attracts them is still not known.
Not all Nepenthes species feed only on animals. N. ampullaria seems to catch a good amount of dead plant parts and faeces falling from the forests canopy, and N. lowii possibly feeds on birds excrements. These plants produce a huge amount of nectar on the underside of it's lid. Birds like nectar, and the peristome of the pitcher is an ideal place to sit on and feed, while the wide pitcher opening collects the birds excrements.

The prey

The pitchers are designed as traps for small animals but some have learned not only to survive but to live there. The fluid is a habitat for a variety of specialised larvae of mosquitoes which can be found only in Nepenthes pitchers. There are also flies and midges, a specialised crab spider (Misumenops) hunts in the pitchers, some frogs lay their eggs there, and even a terrestrial crab can sometimes be found in Nepenthes.
Nepenthes bicalcarata is inhabited by the most fascinating community. Though carnivorous it's a real ant-plant with a mutualistic relationship between the two parners. The ant Camponotus schmitzi are nesting in the hollow tendrils. They rest under the peristome and dive and hunt in the pitcher fluid.

A strange habitat

Misumenops

The spider Misumenops nephicola in a pitcher of N. rafflesiana.

diving ant

The ant Camponotus schmitzi diving and hunting for mosquito larvea in N. bicalcarata

 

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