Credit: MARTIN I. BIDARTONDO

Ghostwort — Cryptothallus mirabilis — is aptly named: it is a liverwort that lives beneath the surface layers in woodland, and rarely comes to human attention. Martin I. Bidartondo and colleagues tell how they have delved into the tangled details of its relationships with other organisms, and brought to light its cheating way of life (Proc. R. Soc. Lond. B 270, 835–842; 2003).

Cryptothallus cannot carry out photosynthesis, and so must have a different energy source. It has long been known that it is associated with certain fungi. In a chain of experiment and inference, in part involving growth of the various players in microcosms, Bidartondo et al. now find that the fungi concerned belong to the Tulasnella group which, in turn, form mycorrhizae — close and mutually beneficial connections (pictured) — with the roots of trees such as birch and pine.

So far, so cosy. But from work with carbon isotopes it turns out that Cryptothallus is a cheat: it gets its carbon supply not from the soil, as once thought, but from the tree via Tulasnella. Instances of such complex relationships are known from other plants and other fungi, but this example greatly widens the field of organisms that can be involved.