The Aristolochiales are a group of paleoherbs, a basal group of flowering plants. There are about 600 to 700 species, most of them in the genus Aristolochia (ca. 500 spp.), and most of the rest in Asarum (ca. 100 spp.).
The majority of the Aristolochiales are tropical, though a number of them range as far north as Canada, Scandinavia, and northern Japan. They may grow as climbing vines, as short creeping herbs, and a few are shrub-like.
Members of this group have attractive leaves and flowers, often with bizarre colors or patterns, and so they are cultivated in gardens. Some oddly shaped flowers have been given names like "bird's head" and "Dutchman's pipe". An example of such a plant is Aristolochia gnaxima, a climbing vine shown at right. In this genus, the sepals are united into a long curving tube which completely surrounds the reproductive structures. Often this tube is mottled or dark-colored, producing a pungent odor that attracts pollinating flies.
Asarum : There are about 100 species of Asarum, today mostly found in temperate regions of North America, Europe, and Asia. Most of these are small creeping herbs with inconspicuous flowers and vestigial petals; the colorful reddish sepals fulfill the role of petals.
Of the living Aristolochiales, only the Chinese Saruma henryi has fully developed petals. Among the remaining genera, vestigial petals are found in some species of Asarum, but the other taxa lack them altogether. In the absence of petals, the sepals have become modified, often with dark colors and unusual shapes. It is thus the sepals that attract pollinating insects.
In addition to the foul-smelling species of Aristolochia that attract flies to pollinate them, other species are important for the survival of butterflies. There has been concern in India (Bhattacharya 1986) that since Aristolochia indica has become endangered, the swallowtail butterfly Tros aristolochae may also be endangered. This butterfly will only lay its eggs on Aristolochia vines, and its caterpillars make defensive use of the toxic chemicals they ingest. In fact most swallowtail caterpillars in the tribe Troidini feed on Aristolochiales foliage (Thorne 1996).
A family description of the Aristolochiaceae is available through the DELTA project. Visit the Tree of Life for current views on the relationships of Aristolochiales.
Pharmaceutical information is available from the Botanical Dermatology Database.
Additional images may be found at the University of Hawaii and Texas A&M.
P. K. Bhattacharya & K. Sarkar. 1986. Impact of the threatened plant, Aristolochia indica L., on the conservation of swallowtail buterfly, Tros aristolochae, in Burdwan. Burdwan Univ. Science Journal 3(1):123-126.
Robert F. Thorne. 1996. The least specialized angiosperms. Pp. 286-313 in Flowering Plant Origin, Evolution, and Phylogeny, D.W. Taylor & L.J. Hickey (eds.). Chapman & Hall, New York.