Hippocrepis comosa Horseshoe Vetch

A procumbent, perennial legume with pinnately divided leaves. The yellow flowers produced in summer give rise to strongly flattened, slightly curved pods with horseshoe-shaped segments. It is a species of chalk and limestone grassland, with a southern distribution in Britain where it has undergone significant losses in the last one hundred years as a result of agricultural improvenments. It is rare in Wales with isolated populations on limestone in north Wales, Gower and mid Glamorgan. Interestingly the Gower population is tetraploid (2n = 28) while the more widely distributed populations on the chalk of south and east England are diploid (2n = 14). Gower plants could be park tundra relict populations descended from plants that occured there in early post glacial periods along with other disjuct Gower species like Draba aizoides, Potentilla crantzii and Veronica spicata. All above ground parts of Horseshoe Vetch contain significant amounts of the highly toxic nitroaliphatic compound, 3-nitropropionic acid, which is an inhibitor of the important mitochondrial enzyme succinate dehydrogense and mitochondial function. This may help to protect the plant aginst herbivores. However Horseshoe Vetch is the food plant for the larvae of the Adonis Blue and Chalkhill Blue butterflies, which must have a strategy for dealing with this toxic phytochemical. If caterpillars are able to sequester this toxin into their tissues, it may render them toxic and provide them with protection against their predators. Since the larvae of both species live in close association with ants, providing them with sugar-rich honey dew in exchange for 'protection', the occurrence of toxic nitroaliphatics in their tissues may protect them from predation by their hosts.

Native