NEPENTHES - pitcher development

Nepenthes x mixta, young upper type pitcher. Note the loop function.

Nepenthes x mixta, lower type pitcher in growth. Thorn + one wing can be seen.

Nepenthes x mixta, left pitcher with recently opened lid and not yet bent back pitcher edge (peristome). Note the two toothed wings on the jugs.

Nepenthes smilesii, neerly mature pitcher, but the lid is still closed.

Nepenthes smilesii, mature pitcher with the lid in a fixed open position.

The development and construction of the Nepenthes pitcher is extremely complicated and far from fully understood. The beginning of the pitcher can be seen as a small flattened ‘bud’ near the tip of the elongated median nerve, which also acts as a tendril. Further development is among other depending on sufficiently high humidity. The starting point is a so-called epiascidiate leaf, i.e. a leaf where the anatomical upper side (the one that faces the stem during the development of the leaf) forms the inner surface of the pitcher, while the underside of the leaf forms the outer side of the pitcher. The underside of the originally flat leaf lamina has thus grown more than the upper side, so that the leaf thereby becomes funnel-, jug- or jar-shaped, and at the same time the leaf edges have grown together. The coalescence often leaves a marked seam or wing, which in other genera with pitfall traps is especially clearly seen in Sarracenia. In Nepenthes, however, there are two wings or ribs on the front of the pitcher. It may have to be interpreted so that the underside of the leaf does not constitute the entire outer side, but that the piece between the wings represents some of the upper side. Although leaves have a certain thickness, they are usually perceived as two-dimensional, but the pitcher of Nepenthes is to that extent three-dimensional, not only apparently because the jug shape, but really, because the lid grows out from the midrib near the thorny leaf tip in a plane more or less perpendicular to the axis of the midrib. A cut perpendicular to the edge of the pitcher edge (the peristome) shows that the edge is T-shaped, where the arms of the T are bent back. In some species, the outer arm is the longest, while in other species it is the other way around. The size of the jug varies from a few cm in the smallest species to over 30 cm long jugs in several of the larger species, where the total volume can be 3 liters, while the amount of digestive fluid rarely exceeds 1 liter. The functional life of the jug also varies from species to species, but is generally shorter than a year and often only a few months.

H. S. Heided-Jørgensen, Dec. 2009. Translated Jan. 2024.