If you go down to the woods today beware of thieving flowers.
Lurking in the woodlands of South America, Martin I. Bidartondo from the University of California, Berkeley, and his colleagues have discovered a new group of vegetal vampires. These plants live by sucking the juices out of others. What is worse, they do so at one remove: fungi are their innocent agents.
Most green plants use sunshine to convert water and carbon dioxide into sugars and starch. Since such honest toil cannot fulfil every need, plants also absorb minerals from the soil through their roots.
An underground cloud of fungal threads surrounds the roots of most land plants. Called mycorrhizae, these fungi trade minerals scavenged from the soil for carbohydrates, made by the plant. Plants' invasion of the land more than 400 million years ago might have been impossible without this close, mutually beneficial association with mycorrhizae.
Such collaborations are always prey to exploitation. Around 400 species of green plant, having lost the ability to make their own food from sunshine, steal it from others that can, through mycorrhizae associated with nearby green plants. Vampire-like, they suck their neighbours' sap.
The technical term for such a parasite, which exerts thievery at one remove, is an epiparasite. Some have beautiful flowers that belie their nefarious natures.
Until now, all known cases of vegetal vampirism involved the ectomycorrhizae, the small group of fungi that produce distinctive fruiting bodies including truffles and chanterelles.
But around 70 per cent of mycorrhizae belong to another group, the arbuscular mycorrhizae. Because these live entirely underground and do not produce mushrooms or other fruiting bodies their obscurity is out of all proportion to their ecological importance.
Now Bidartondo's team have found two cases of epiparasitism involving arbuscular mycorrhizae, both in South America. The discovery suggests more examples should follow shortly.
One case is the lily-like flower Arachnitis uniflora, an epiparasite of trees in the temperate forests of Argentina. This uses just a few mycorrhizae to steal sustenance from a variety of sources, including the southern beech (Nothofagus) - extreme specialization is a hallmark of a true parasite.
The other case involves plants called Voyria and Voyriella, relatives of gentians that live in the tropical rainforest of French Guiana. Again, these epiparasites exploit only a handful of mycorrhizae.
Henry Gee is a Senior Biological Sciences Editor at Nature.
Bidartondo, M. et al. Epiparasitic plants specialized on arbuscular mycorrhizal fungi. Nature, 419, 389 - 391, (2002).