Plants belonging to the genus Nepenthes often are called pitcher plants or monkey cups. Pitcher plants are insectivorous, or insect-eating, plants that have tubular leaves that resemble a cup or pitcher. Darlingtonia is another genus of insectivorous plants, and frequently Nepenthes plants are confused with Darlingtonia plants. Where Nepenthes plants are not native, growers usually raise them as greenhouse or indoor plants.
Of the 450 known species of insectivorous plants, more than 70 species belong to the Nepenthes genus. Some botanists contribute about 90 species to this genus. They are evergreen perennials from parts of Madagascar, southeastern Asia, Queensland, and other areas in these regions. Generally, they grow in moist, acidic soils in open areas, such as grasslands and often in forests. Many species grow epiphytically, or non-parasitically, on trees.
The pitchers are leaves that are tubular with a hollow pouch. Usually, the leaves are lance- or strap-shaped, ranging from 2 to 26 inches (about 5 to 65 cm) long, depending on the species, hybrid, or cultivar. Each leaf has a stretched-out midrib that acts as a tendril to support the plant. The pitchers grow at the end of some of these tendrils. The pitchers may range from 2 to 14 inches (about 5 to 35 cm) and taller.
Although these plants receive most of their nutrients from the soil and photosynthesis, they capture and devour insects. Some parts of the plant, including the leaves, have glands that emit chemicals that attract the unsuspecting insects. When the insects fall into the pitcher, they drown in a fluid secreted by the plant. Enzymes in the fluid break down the insects, and the plant digests them.
With so many different species and variations, the pitchers vary in size, color, and shape. N. phyllamphora has pale, reddish-green pitchers that are about 6 inches (about 15 cm) long and 1.5 inches (about 4 cm) across and have narrow frontal wings. In contrast, N. veitchi has hairy yellow-green to red pitchers that have very wide rims and fringed wings. The pitcher of N. rafflesiana is pale green, marked with brownish-red color, and sports a striped rim. It has large, toothed wings with slightly hairy edges.
The pitchers may even differ within the same species. For example, N. mirabilis var. echinostoma has a tall, slender, pale green pitcher that is marked with chocolate-red. N. mirabilis var. globosa has a stout bright red pitcher. The N. rajah has very large pitchers — up to 14 inches (about 35 cm) long — that can catch mice, rats, and small birds.
Pitcher plants are tropical plants and normally do not tolerate frost. Generally, in greenhouses, growers are able to control their environment. Some species are very touchy about temperature fluctuations. For example, some botanists suggest that species and hybrids from areas near sea level require daytime temperatures of about 75°F (about 24°C) and nighttime temperatures of about 60°F (about 15°C). Highland species have lower temperature requirements.
The flowers are unusually odd and resemble insects. They are tiny, petal-less, and often have green or brown sepals. Generally, the flowers are borne on spike-like racemes. Racemes are unbranched flower stalks with the youngest blooms near the tip.
In the wild, Nepenthes plants have a mutualistic symbiotic relationship with some insects. The insects, usually ants, eat the undigested food in the pitcher. Often ants pull larger pieces to the rim, and as they eat small pieces drop back into the pitcher. The plant finds these smaller bits easier to digest.