In some carrion flowers the insects are lured into dark openings leading to the putrefying interior where they become trapped among the floral organs. This strategy insures cross pollination, especially when the male anthers release pollen several days after the female stigma is no longer receptive. When the imprisoned insects are allowed to leave they are given a thorough dusting of fresh pollen to be taken to a different plant. One of the classic insect-trapping carrion flowers is the European Dutchman's pipe (Aristolochia clematitis), a member of the birthwort family (Aristolochiaceae). The unusual common names are derived from the curious blossoms with a shape reminiscent of Sherlock Holmes' pipe, and an old herbal remedy. Some species in this family have aromatic roots that were reputedly used as a purgative to induce labor, a questionable practice that is not recommended. The curious blossoms of some species superficially resemble a human fetus in the womb, and the plants were once thought to facilitate child birth. During medieval times, various ailments were treated with plants that resembled certain afflicted parts of the body. This practice was called the "Doctrine of Signatures," and became the basis of medical treatment for centuries to come. The striking, tubular flower of Dutchman's pipe is held upright as it emits a foul, pungent odor. Small gnats land on the vertical upper calyx surface but slip down through the floral tube and into the inflated "pipe chamber" due to slippery wax granules on the inner surface. Dense, downward-pointing hairs in the floral tube prevent the gnats from climbing out. During their incarceration the gnats receive rations of nectar. Several days later, when the anthers release pollen, the jail hairs wilt and the flower tilts horizontally, allowing the pollen-laden gnats to walk out of their prison, and into another receptive floral trap on a different plant.

There are approximately 350 species of Aristolochia, mostly from tropical regions of the world. Many species have ingenious insect traps and malodorous, often nauseating stenches when the blossoms first open. One of the largest and most bizarre flowers on earth is the Brazilian Dutchman's pipe (A. gigantea). Although it belongs to a genus of carrion flowers, its blossom does not smell like rotting flesh or feces to the human nose, but still emits an odor attractive to small flies. The showy maroon petal-like calyx is the size of a large dinner plate (30 centimeters) across), with an "inviting" orifice leading into an inflated, bladder-like trap. Another unusual Dutchman's pipe native to northern California (A. californica) has much smaller blossoms that are pollinated by fungus gnats. Species of Aristolochia (often called pipevines) are the host for the pipevine swallowtail, a beautiful blue butterfly with bright red caterpillars.

Pipevine swallowtail (Battus philenor): Swallowtail family (Papilionidae).

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4. California Pipevine (Aristolochia californica) In Full Bloom

A Dutchman's pipe (Aristolochia californica) native to the Coast Ranges of Central and Northern California, and foothills of the Sierra Nevada. This California species is pollinated by fungus gnats.

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