Dioecious, mainly insectivorous pitcher-bearing vines, typically climbing by means of tendrils, or subscandent, prostrate or occasionally erect or shrubby, young plants rosetted, leaves congested along main axis, internodes lengthening as plants mature. Leaves alternate, spiral or rarely distichous, petiolate, sessile or amplexicaul, in outline generally elliptic, oblong or linear, rarely orbiculate, apices acuminate, acute or obtuse; the leaf unit comprises a lamina, emergent tendril and pitcher, the latter developing from the distal portion of the tendril and comprising an ascidium (pitcher) with a variably glandular inner wall that facilitates the digestion and assimilation of trapped organic material, surmounted by an overarching to reflexed operculum (lid) with a spur at its base on the outside of the pitcher and, usually, a conspicuous peristome (recurved rim) bearing a characteristic regular pattern of radial ridges which, on the inner edge, form fine terminal processes (teeth); pitchers of rosette leaves generally robust, facing tendril and resting on the ground, those of vining stems more gracile, facing away from tendril, the tendril itself often coiled, wrapping around supports to aid climbing. Inflorescence a panicle, in most species reduced to racemose botryoid form, bracteate or not, terminal, appearing lateral owing to continued growth of main axis from development of the subtending axillary bud, flowers borne from partial peduncles arising from rachis, opening acropetally. Flowers unisexual, actinomophic, apetalous, perianth consisting of four free, decussate tepals in two whorls, adaxial surfaces bearing usually large multiseriate nectar glands. Male flowers bearing (4–) 8–24 stamens connate in a central column, anthers 2-locular, longitudinally extrorse, pollen united in tetrads, inaperturate, spinulose–psilate. Female flowers bearing a superior compound ovary, usually comprising 4 fused carpels with as many locules; ovules numerous, axile or laminar, anatropous; stigma apical, discoid, lobate, sessile or on very short, stout style. Capsule dehisces longitudinally and loculicidally into 4 valves, seeds fusiform to filiform, 5–25 mm long.
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Lianas or shrubs to 20 m, sometimes only weakly woody, dioecious, carnivorous. Stem simple or branched, erect, climbing, or procumbent, cylindric or triangular in cross section, glabrous or pubescent. Leaves alternate, petiolate or sessile; midvein prolonged into a tendril, apex of tendril usually developing into a dimorphic pitcher with a lid usually projecting over mouth and a spur inserted at base of lid. Pitchers toward base of plant ovoid, facing inward, with 2 fringed wings, tendril ventral, uncoiled; pitchers toward apex of plant cylindric or funnelform, facing outward, wings generally unfringed or reduced to ridges, tendril dorsal, coiled. Inflorescence terminal (appearing leaf opposed because of continued axillary growth), racemose, or with secondary branches 2-flowered or cincinni, usually sparsely bracteate. Flowers regular; perianth in 1 whorl of (3 or)4 tepals. Male flowers with 4-24 anthers; filaments united into a column; pistils inconspicuous. Female flowers with inconspicuous anthers; pistils (3 or)4; ovary superior, stipitate or not, ovoid-globose or tetragonal-terete, rarely obdeltoid, (3 or)4-loculed; placentation axile; ovules numerous, in many rows; style very short to obsolete; stigma disclike, (3 or)4-lobed. Capsule (3 or)4-valved, leathery or woody, loculicidally dehiscent. Seeds numerous, usually hairlike; embryo straight; endosperm fleshy.
The greater proportion of Nepenthes are either ultramafic endemics or largely restricted to mafic substrates or iron rich surface laterites with associated open canopies, most of the remainder occurring on similarly nutrient-poor humic, arenaceous or granitic substrates. In Australia, native Nepenthes are largely restricted to open, perhumid, seasonally wet habitats such as swamps and the margins of river courses, typically on clay laterite or surface sandstones and soils derived thereof.
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