Nepenthes x ventrata is a natural hybrid between N. ventricosa and N. alata, both occurring in all the major Philippine islands. A trapped insect marks the liquid surface in the pitcher.           

Nepenthes x ventrata is a natural hybrid between N. ventricosa and N. alata, both occurring in all the major Philippine islands.

NEPENTHES – pitcher plant, is a genus of carnivorous plants in the pitcher plant family (Nepenthaceae) with approx. 120 species in tropical-subtropical rainforest. The name was first used by Linnaeus and is believed to come from Greek, where penthos means suffering. The main distribution is in SE Asia. In the peripheral areas, there are also endemic species in Madagascar (2) in northern Queensland (2) and 1 species in the Seychelles, Sri Lanka, New Caledonia and in northern India respectively. The most widespread species N. mirabilis has isolated occurrences at the base of the Cape York Peninsula (Queensland) and on the Caroline Islands of Palau and Yap. The current scattered distribution can be partly explained as a result of the breakup of the supercontinent Gondwanaland.

     They are lianas or epiphytic semi-shrubs with spreading, leathery and apparently entire-margined leaves. Another view, however, is that the flat part of the leaf is a winged petiole and the pitcher at the end of the midrib the actual leaf plate. In many species, the lower part of the stem is lignified. The flowers are unisexual and sit in long clusters on male and female plants; they have a small greenish, four-numbered blossom and either 8-14 stamens or four fused carpels. The flowers contain nectar and are pollinated primarily by flies and moths. The fruit is a capsule and the seeds are dispersed by the wind.

     In healthy plants, the midrib of the leaves is elongated into a strong tendril that carries a pitcher or jar-shaped organ at the tip. The pitchers vary from species to species and along the shoot of the individual species. Each species produce at least two types of pitchers, lower and upper pitchers, of different shapes and sizes. The largest pitchers are found in N. rajah, where the length can be 38 cm, the width 20 cm, and they hold up to 1 liter of very acidic, enzyme-containing digestive fluid. The pitcher is equipped with a lid. It appears as a transverse fold on the midrib just below the leaf tip, which can be seen as a small thorn located between the lid and pitcher. The lid is closed hermetically to the pitcher rim during pitcher development, while the digestive fluid is simultaneously secreted from digestive glands in the pitcher wall. The pH is measured at 2.5 in the closed jug, but then rises slightly under the influence of prey from outside and rainwater. The enzymes protease, ribonuclease, lipase, esterase and acid phosphatase as well as N. ampullaria amylase have been found in the closed jug, and the jug liquid has a low surface tension. In the full-grown jug, the lid is open in a fixed position more or less bent over the mouth of the jug. In some species, it provides an umbrella effect that can prevent the pitcher fluid from being diluted too much by rainwater. The pitcher functions as a passive pitfall trap, as no movement is involved in capturing the prey.

     Insects and other small animals are attracted by nectar from glands on the edge of the pitcher (the peristome, the collar), but if they fall into the pitcher, they drown and are dissolved by protein-splitting enzymes, after which the nutrients are absorbed through the digestive glands at the bottom of the pitcher. In species with large pitchers, young birds, frogs and small rodents are occasionally caught. A single species, N. ampullaria is more herbivore (vegetarian) than carnivore. Its jugs stand on the ground, and the lid is tilted all the way back, so that the jugs can collect fallen organic matter such as withered leaves and flowers. It is the only species where the starch-splitting enzyme amylase has been detected in the pitcher fluid.

     The inside of the jugs is designed so that the prey has difficulty gaining a foothold and thus escaping. At the top is the surface, i.e. the epidermal cells, covered with loose waxy scales that fall off when touched. In this zone, there are also inactive highly modified slit openings, where the stomata guard cells are obliquely sunk into the surface, so that insect feet cannot immediately use them for a foothold. Further down, the epidermal cells are covered by a mirror-smooth layer of wax, and all glands are also sunken into the surface and covered by an overhanging ‘roof beard’, so that it is difficult to get a foothold here, too.

     Some animals, especially spiders and mosquito larvae, have their natural habitat in the pitchers, where they benefit from prey that would otherwise benefit Nepenthes. Some spiders lie in wait in the jug mouth, other species spin their webs across the jug just above the liquid level. Larger animals visit the jugs as a kind of grave robber. This applies, for example, to the small primate, Tarsius spectrum, from Borneo. Here, as a defense, N. bicalcarata has developed a pair of deadly-looking ‘fangs’ under the lid, so that the pitcher’s mouth looks like an open snake gap. It is believed to deter Tarsius, who fear snakes. In addition, a number of microscopic organisms such as blue-green algae, protozoa etc. have their permanent habitat in the jugs. It is not known what makes these organisms immune and resistant to the digestive fluid.

Click on the images below and get more information.

Nepenthes ampullaria – Flowering

Nepenthes x mixta – Pitcher types

Nepenthes x mixta – Pitcher development

Nepenthes x mixta – Digestive glands

Nepenthes x mixta – The peristome (pitcher edge)

Nepenthes x mixta – Wax scales on the inside of the pitcher

Nepenthes alata – One of the parents of N. ventricosa

Nepenthes ampullaria – Vegetarian among carnivorous plants

H. S. Heide-Jørgensen, Nov. 2009. English translation Dec. 2023