Bog asphodel and toxic saponins

Bog asphodel (Narthecium ossifragum) flowering in late June, Galicia, Spain

Bog Asphodel, Narthecium ossifragum,is a perennial herb (5 -40 cm tall) which typically grows on short wet grasslands on acid soils. It occurs in the British isles, Scandinavia, the Netherlands, Belgium, Germany, France, Northern Spain and East Portugal. I first got to know it in the form shown below, when it is in fruit, at the end of summer or early autumn.

Bog asphodel (Narthecium ossifragum) fruiting in late September. Galicia, Spain

It looks rather different when it is in flower (below), for example in June.

Bog asphodel (Narthecium ossifragum) flowering in late June, Galicia, Spain

I did not know, until I started researching it for this blog, that this flower can cause some diseases in herbivores. For example, it can cause photosensitisation, a serious skin condition of sheep called alveld: a disease that causes internal damage, a swollen face and hypersensitivity to light. The effects are described here, from Scotland. It is a pity because it such a pretty plant.

Bog asphodel (Narthecium ossifragum) flowering in late June, Galicia, Spain

However, its toxic properties seem to vary, and it is said to be entirely benign in some locations, but toxic to cattle and sheep in others causing photosensitivity and sudden death. The effects appear to be due to the presence of saponins, compounds like sarsasapogenin (below), which are produced by the plant to avoid being eaten! I.e. antifeedants. Cattle are said to be unwilling to eat N. ossifragum because it is toxic.

Chemical structure of sarsasapogenin
Bog asphodel (Narthecium ossifragum) fruiting in late September

Plants contain a variety of toxic compounds that affect the behavior and health of wild and domestic animals. Part of the age old struggle between herb and herbivore! Many of the toxins in plants are however, degraded and transformed so that herbivores can feed on plants with toxins and avoid any ill effects.

References

Díaz, A. E. C., Herfindal, L., Rathe, B. A., Sletta, K. Y., Vedeler, A., Haavik, S., & Fossen, T. (2019). Cytotoxic saponins and other natural products from flowering tops of Narthecium ossifragum L. Phytochemistry164, 67-77.

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