Aristolochia clematitis L. (Aristolochiaceae)



Aristolochia clematitis growing in Oxford Botanic Garden. Coloured engraving of Aristolochia clematitis from Sowerby's 'English Botany' (1797, t.398).

Birthwort, a twining plant introduced to Britain from continental Europe because of its medicinal value, is found wild near Oxford around the ruins of the Benedictine Abbey at Godstow, resting place of Henry II's mistress 'Fair Rosamund'. Through the Doctrine of Signatures, birthwort, with its birth canal-shaped flower, has been associated with the female reproductive system for millennia. The English folksong Tamlyn refers to a bitter herb that will twine away a babe. Birthwort, together with other Aristolochia species, has found multifarious uses in traditional medicinal systems, including as an emmenagogue and abortifacient.

Ancient use, combined with the adjective 'natural', is used to send powerful advertising messages that medicines are effective and devoid of harmful chemicals. Throughout centuries, vast profits have been amassed with such claims, whilst graveyards, pyres and ossuaries bear witness to the other side of the twin fallacies of antiquity and naturalism. In the late 1950s a chronic kidney condition was described from certain Balkan farming villages near the Danube. The condition was not inherited and villagers only began to show symptoms some 15 years after becoming resident, suggesting an environmental cause. Recently, strong evidence has shown that cumulative dietary poisoning by aristolochic acid, a powerful carcinogen and kidney toxin, is important in the development of the condition and the associated cancer. Aristolochic acid is likely to come from birthwort, a local field weed, contaminating cereal grains used to make bread. Despite the dangers of their use, Aristolochia species continue to be used as traditional medicines.

Birthwort belongs to one of the basal flowering plant families, yet it has an elaborate pollination mechanism, as shown in 1793 by the German theologian and naturalist Christian Sprengel in Das entdeckte Geheimnis der Natur im Bau und in der Befruchtung der Blumen. Overlooked during his lifetime, Sprengel's work is the foundation of our understanding of the roles of insects as pollinators. Hermaphrodite, tubular birthwort flowers have two discrete stages; male and female. Flies are attracted to the foetid scent of the female stage, slide into the base of the flower and are trapped there by rows of forward-pointing hairs in the tube throat. The flies feed on nectar and deposit pollen on the stigmatic surfaces. During the male stage, which may last two days, the trapped flies become dusted with pollen. The fly is released when the throat hairs shrivel and the fly crawls free, only to enter another flower.

Further reading

Grollman AP et al. 2007. Aristolochic acid and the etiology of endemic (Balkan) nephropathy. Proceedings of the National Academy of Sciences USA 104: 12129-12134.

Oelschl├Ągel B et al. 2009. Structure and biomechanics of trapping flower trichomes and their role in the pollination biology of Aristolochia plants (Aristolochiaceae). New Phytologist 184: 988-1002.

Stephen Harris