OXALIDACEAE

The Oxalidaceae or sorrel family comprises some 800+ species of herbs, shrubs and trees found in tropical and temperate regions of the world. They have alternate or pinnate leaves, numerous symmetrical flowers, and fruits in the form of capsule or berries. Some species exhibit a phenomenon called nyctinasty, the leaves droop and 'sleep' during the night. The starfruit tree (Averrhoa carambola) even exhibits thigmonasty, its leaves droop when touched!  Oxalidaceae plants contain a simple organic acid called oxalic acid, which is responsible for their sour taste. Oxalic acid is poisonous because it can form insoluble salts like calcium oxalate. When calcium oxalate accumulates in the kidney, it forms kidney stones.


The starfruit is edible but it contains a neurotoxic amino acid called caramboxin. In patients with kidney disease, caramboxin can quickly reach toxic level. It causes persistent hiccup, seizure and death. Even healthy individuals can develop symptoms of caramboxin toxicity when large quantities of starfruit are consumed on an empty stomach. Death by starfruit is rare, but patients with kidney failure are forbidden to consume starfruit in any quantities.

 

Starfruit (Averrhoa carambola)