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Sarracenia

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Sarracenia is a genus of carnivorous plants indigenous to the eastern seaboard of the United States, Texas, the Great Lakes area and southeastern Canada, with most species occurring only in the south-east United States (only S. purpurea occurs in cold-temperate regions). The plant's leaves have evolved into a funnel or pitcher shape in order to trap insects.

The plant attracts its insect prey with secretions from extrafloral nectaries on the lip of the pitcher leaves, as well as a combination of the leaves' color and scent. Slippery footing at the pitcher's rim causes insects to fall inside, where they die and are digested by the plant with proteases and other enzymes.

Description

Sarracenia are herbaceous perennial plants that grow from a subterranean rhizome, with many tubular pitcher-shaped leaves radiating out from the growing point, and then turning upwards with their trap openings facing the center of the crown. The trap is a vertical tube with a 'hood' (the operculum) extending over its entrance; and below it the top of the tube usually has a rolled lip (the peristome) which secretes nectar and scents. The hood itself frequently produces nectar too, but in lesser quantities.

The inside of the pitcher tube, depending on the species, can be divided into three to five distinguishable zones: zone 1 is the operculum (or hood), zone 2 is the peristome and rest of the trap entrance, while zones 3 and 4 (which in some species are combined) and 5 (only present in S. purpurea) are further divisions of the actual tube. Each of these zones has a specific function, with corresponding morphophysiological characteristics.

  • Zone 1: Operculum. In most species the operculum covers at least part of the pitcher has an opening, preventing rain from excessively filling the pitcher, which would result in the loss of prey and dilute the digestive fluid. The operculum also serves to guide prey to the pitcher opening, using a combination of color, scent, and downward-pointing hairs to lead insects toward the trap entrance. Some species, specifically S. minor and S. psittacina, have opercula that hang low over the pitcher entrance. These are also studded with chlorophyll-free patches, translucent "windows" which confuse prey into attempting to fly through the operculum, thereby causing them to cascade down the pitcher tube. (A similar, better-developed mechanism is found in the closely related Darlingtonia californica).
  • Zone 2: Peristome and trap entrance. This zone is composed mainly of the peristome, which produces copious amounts of nectar, luring insect prey to land or crawl onto the perilous footing surrounding the pitcher trap. This zone also includes the waxy upper portion of the pitcher tube. Footing on this zone is especially treacherous, as the waxy deposits on surface of this zone cause unwary insects to lose their footing and tumble into the pitcher depths.
  • Zone 3: Located below Zone 2, this zone features a leaf surface with non-existent footing, as well as a coating of ultra-fine, downward pointing hairs. Insects that have made it this far lose any chance of escape. It is also studded with digestive glands, which secrete digestive enzymes into the digestive fluid.
  • Zone 4: This is the final zone in most species. It is filled with digestive fluids, and readily absorbs nutrients released from the insects by the work of the digestive enzymes and bacteria in the pitcher fluid. Along with more digestive glands, this zone features a thick coating of coarse downward pointing hairs, which makes escape from the digestive fluids impossible.
  • Zone 5: This zone, located below Zone 4 and found only in S. purpurea, is smooth, glabrous, lacks glands, and does not serve as an absorptive zone. Its function is unknown.

Carnivorous mechanism

All Sarracenia trap insects and other prey without the use of moving parts. Their traps are static and are based on a combination of lures (including color, scent, and nectar) and inescapability – typically the entrances to the traps are one-way by virtue of the highly adapted features listed above.

Most species use a combination of scent, waxy deposits (to clog insect feet) and gravity to topple insect prey into their pitcher. Once inside, the insect finds the footing very slippery with a waxy surface covering the walls of the pitcher. Further down the tube, downward-pointing hairs make retreat impossible, and in the lowest region of the tube, a pool of liquid containing digestive enzymes and wetting agents quickly drowns the prey and begins digestion. The exoskeletons are usually not digested, and over the course of the summer fill up the pitcher tube.

Only S. purpurea normally contains significant amounts of rainwater in its tubular pitchers. It is a myth that all species contain water. In fact, the hoods of the other species help to keep out rain water in addition to keeping flying prey from escaping.

S. psittacina, the parrot pitcher, uses a lobster-pot style trap that will admit prey (including tadpoles and small fish during floods) but not allow it to find its way out; and sharp inward-pointing hairs force the victim gradually down to the base of the pitcher where it is digested.

Potential narcotic function of coniine

Coniine, a toxic alkaloid also present in poison hemlock, was first detected in the nectar of S. flava. and has since been detected in 7 other species of Sarracenia. While it was demonstrated that concentrated extracts from S. flava could paralyze ants, it has not been demonstrated that coniine has narcotic effects on insects at the concentrations naturally present in pitchers of S. flava. Other authors hypothesize that coniine may function as an attractant for insects, or may function both as an attractant and a narcotic.

Flowers and seeds

Flowers are produced early in spring, with or slightly ahead of the first pitchers. They are held singly on long stems, generally well above the pitcher traps to avoid the trapping of potential pollinators. The flowers, which depending on species are 3–10 centimeters in diameter, are dramatic and have an elaborate design which prevents self-pollination. It consists of five sepals superintended by three bracts, numerous anthers, and an umbrella-like five-pointed style, over which five long yellow or red petals dangle. The whole flower is held upside-down, so that the umbrella-like style catches the pollen dropped by the anthers. The stigmas are located at the tips of the umbrella-like style. The primary pollinators are bees. Bees searching for nectar must force their way past one of the stigmas to enter the chamber formed by the style. Inside, they will inevitably come in contact with a lot of pollen, both from the hanging anthers and from the pollen collected by the style. Upon exiting, the bees must force their way under one of the flap-like petals. This keeps them away from the stigma, avoiding self-pollination. The next flower visited receives on its stigmata some of the first flower's pollen, and the cycle continues.

Floral formula: Ca5 Co5 A∞ G(5)

The flowers of almost all species are scented. The scent varies, but is often strong and sometimes unpleasant. S. flava has an especially strong odor resembling cat urine.

Flowers generally last about two weeks. At the end of the flowering period, the petals drop and the ovary, if pollinated, begins to swell. The seed forms in five lobes, with one lobe producing significantly smaller numbers of seeds than the other lobes. On average, 300–600 seed are produced, depending on species and pollination success. Seed takes five months to mature, at which point the seed pod turns brown and splits open, scattering seed. The seeds are 1.5–2 mm in length and have a rough, waxy coat which makes it hydrophobic, possibly for seed dispersal by flowing water. Sarracenia seed requires a stratification period to germinate in large numbers. Plants grown from seed start producing functioning traps almost immediately, although they differ in morphology from adult traps for the first year or so, being simpler in structure. Plants require 3–5 years to reach maturity from seed.

Growth cycle

Pitcher production begins at the end of the flowering period in spring, and lasts until late autumn. At the end of autumn, the pitchers begin to wither and the plants produce non-carnivorous leaves called phyllodia, which play a role in the economics of carnivory in these species. Since the supply of insects during winter is decreased, and the onset of cold weather slows plant metabolism and other processes, putting energy into producing carnivorous leaves would be uneconomical for the plant.

Genetics

The genus has been found to have a Chromosome number of 2n=26, though some earlier studies had found that number to be 2n=24.

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