INHS report January February 1995

Species Spotlight: Pitcher Plants

The pitcher plant, Sarracenia purpurea, has turned the tables on animals--eating them rather than being eaten. Pitcher plants are classified as carnivorous rather than insectivorous because they consume not only insects but also isopods, mites, spiders, and an occasional small frog. While carnivory helps the plants remain vigorous, grow larger, and produce more flowers, it does not appear essential for the survival of individual plants. This unusual life-style has evolved as a means of obtaining nutrients in places otherwise deficient in them. In addition to phosphorus and nitrogen, pitcher plants obtain vitamins and other trace minerals from their prey.


A pitcher plant patiently awaiting its next meal.

Pitcher plants have a rosette of tubular-shaped green leaves streaked with purple and red. In June, nodding umbrella-shaped maroon flowers appear on a stalk 1 to 2 feet above the plants. When closed, the flowers resemble apples on a stick. Listed as an endangered species in Illinois, pitcher plants are found in bogs, fens, and on calcareous floating mats--habitats that are found in the northeastern corner of Illinois, where they are rare.

The leaves of the pitcher plant are not flat like those of most plants; they have become highly specialized, having evolved a passive way to catch prey -- a pitfall trap. The leaf edges have curled around and fused to form a liquid-holding vessel, similar in shape to a cornucopia. The leaves grow from a basal rosette and a "keel" provides structural reinforcement to each leaf so that the opening is always upright. The modified leaves perform the task of taking in nutrients required for photosynthesis. Insects are attracted to the colorful leaf rosettes that resemble flowers; the red lip of the "pitcher" is particularly attractive as a landing zone. Red veins that lead downward are baited with nectar. While following this lure, prey reach the curve of the tube, which is lined with fine hairs, all pointing downward. A slip and the animal is soon speeding to its impending doom. It plummets into the pitcher, which contains rain, dew, and a digestive enzyme that soon dissolves the victim.

Root systems of carnivorous plants tend to be weak and poorly developed. Since the roots function almost entirely as support, the highly acidic bog water doesn't seem to bother them.

Habitat destruction and illicit collecting are the biggest threats to the survival of the endangered pitcher plant in Illinois.

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