Mayapple
A herbaceous member of the berberis family, from the north east of the United States, Podophyllum peltatum emerges in spring with its leaves folded downwards around a pale, fleshy stem. The leaves eventually expand to around 15 cm in diameter, giving the plant an umbrella-like silhouette. The generic name Podophyllum is a shortened version of Anapodophyllum, meaning 'leaves shaped like the foot of a duck', the individual segments having a vague resemblance to the shape of a webbed foot.
Each stem bears a maximum of two leaves. Those with one leaf will fail to flower, but those with two leaves produce a white flower, whose many stamens have conspicuous yellow anthers. The flowers are borne in the leaf axil and are hidden when the plant is viewed from above. Flowers are followed by pendulous, oval fruits, which are green at first then become yellow when ripe. The appearance of the fruits has inspired common names such as mayapple and ground lemon. Unripe fruits, leaves and roots are poisonous.
Not an obvious choice as a garden plant because of the concealed flowers, mayapple nevertheless provides interest in a woodland garden, where it thrives in moist, shady spots, its bold foliage contrasting with more delicate ground-layer plants that might be planted around it.
The medicinal properties of toxic plants are a matter of dose. Too much and the plant can be lethal, just enough and the plant can be curative. Native Americans made extensive use of mayapple extracts as medicines. Today, such extracts are used externally against warts and tumours.
The active substance in mayapple is podophyllotoxin, which was first isolated in 1880. It prevents cell division and is an antiviral substance with a multiplicity of medicinal uses. Pure podophyllotoxin is too dangerous for clinical use, but semi-synthetic drugs have been developed from it. Attempts to make synthetic podophyllotoxin have been unsuccessful, consequently, it is isolated from plant material, before being processed into chemotherapy drugs such as etoposide. Etoposide has been used as a chemotherapy drug since the 1990s.
Evidence shows that chemicals derived directly from plants, or through modification of natural plant products, have proven successful in the search for new drugs to cure our ailments. The observation that more than 40% of chemotherapy drugs are either natural products or their semi-synthetic derivatives are sobering in the light of the threats that continue to be faced by the world's plant species.
Further reading
Saslis Lagoudakis CH et al. 2012. Phylogenies reveal predictive power of traditional medicine in bioprospecting. Proceedings of the National Academy of Sciences of the United States of America 109: 15835-15840.
Moraes RM et al. 2000. The American mayapple revisited - Podophyllum peltatum - still a potential cash crop? Economic Botany 54: 471-476.
Ruth Calder