Sarraceniaceae – Carnivory, Genera
qiazhan English name: Sarraceniaceae
Sub Title:
Sarraceniaceae, family of carnivorous pitcher plants in the order Ericales, native to North and South America. These low-growing perennial herbs are notable for their modified pitcherlike leaves, which serve as pitfall traps to ensnare and digest insects and other small prey. The family consists of three genera: Sarracenia, with about 10 species; Darlingtonia, with one species; and Heliamphora, with some 23 species. (The pitcher plants in the family Nepenthaceae are limited to the Old World.)
The Sarraceniaceae are unlike any other plants in the Western Hemisphere. They derive their common name from their hollow tubular leaves, which can take the form of a trumpet, a pitcher, or an urn. These leaves passively capture prey that are lured to the leaf’s mouth by its glistening surfaces or unusual colouration and transparent patches. If an insect or other organism falls into the pitcher, stiff downward-pointing hairs and slippery walls prevent it from crawling back out. Exhausted, the animal eventually drowns in the liquid at the bottom of the pitcher. Protein-digesting enzymes and bacteria break down the insect’s body, allowing nitrates and other useful nutrients to be absorbed by the plant to supplement the poor soil conditions of its environment.
Members of Sarraceniaceae commonly inhabit bogs, swamps, wet or sandy meadows, and savannas where the soils are water-saturated, acidic, and deficient in nitrogen or phosphorous. Instead of an upright aboveground stem, the pitcher plant usually has a short, round, horizontal rhizome (underground stem) from which leaves radiate outward and upward. The mature rhizome, which is 8–30 cm (3–12 inches) long, grows for 10 to 30 years, depending on the genus. Most members of the family produce a crop of pitcher leaves in the spring and a second crop of leaves in the fall. The leaves vary in colour from yellow green to dark green suffused with red. The leaves are clearly adapted to function like flowers in attracting insects: they are flowerlike in their striking colour patterns and shapes, and, during their active period in the summer, they exude nectar containing fructose, which is highly attractive to some insects. Some species, including the purple pitcher plant (S. purpurea), have been found with salamanders in their pitchers. It is likely that such incidental victims are attracted to the insects that are enticed by the pitchers and provide a boost of nutrition for the plants.
Besides having flowerlike leaves, all members of Sarraceniaceae produce flowers that are showy and have an agreeable scent. The nodding flowers are insect-pollinated, usually by bees, and are usually borne on long stalks to keep the pollinators away from the deadly pitchers. The flowers’ petals are usually five in number, and the stamens are numerous and shed pollen copiously. The fruits are dry capsules that shed their seeds. Some species propagate vegetatively; in Darlingtonia, and less often in Sarracenia, buds arise at nodes (stem joints) in the rhizome and grow into new plants, giving rise to slowly spreading colonies.
Known as trumpet pitchers, the genus Sarracenia is confined to eastern North America and is concentrated in northern Florida and the southern parts of Georgia and Alabama. The yellow pitcher plant (S. flava) is probably the most abundant species, though the purple, or common, pitcher plant (S. purpurea) has a much wider range—from Labrador and Great Bear Lake (near the Arctic Circle) to subtropical Florida. The cluster of leaves produced by species of Sarracenia ranges in size from 10 cm (4 inches) in the sweet pitcher plant (S. rubra) to more than 120 cm (4 feet) in the crimson pitcher plant (S. leucophylla). The habitat of Sarracenia species ranges from sand and gravel along stream banks to wet meadows and savannas. Most of the species thrive in full sunlight.
The other North American genus, Darlingtonia, includes only the cobra plant (D. californica). It ranges from Oregon to northern California and thrives in redwood and red fir forests up to 2,000 metres (6,000 feet) above sea level, where temperatures remain below about 18 °C (65 °F). Its overarching spotted hood and a unique landing ramp that extends from the top of the curiously twisted tubular leaf account for its common name. Using the landing projection, insects often enter the mouth of the pitcher from the side of the domed hood. Trapped insects often fly against the hood’s translucent “windows” and eventually fall into the liquid at the pitcher’s bottom.
The third genus, Heliamphora, grows in the rainforest mountains of Brazil, Guyana, and Venezuela. Often called sun pitchers or marsh pitcher plants, Heliamphora species form cushions on ridge crests and mingle with peat moss in swampy depressions. The stems of some species rise to more than 120 cm (48 inches) and are branched and slightly shrubby. Their pitchers attain a height of 50 cm (20 inches).
