FABACEAE

The Fabaceae (synonymous with Leguminosae) or bean family comprises some 10,000+ species of herbs, shrubs, climbers, and trees of cosmopolitan distribution. This large family is characterised by simple, alternate, or pinnate leaves, irregular butterfly-like flowers, fruits in the form of a legume (a pea pod), and roots that harbour symbiotic relationship with nitrogen-fixating bacteria. Many Fabaceae species are cultivated as food crops such as the ground nut, soybean, alfalfa, peas and lentils, as well as licorice (sweetener) and tamarind (tangy souring agent).

Fabaceae elaborate a plethora of plant toxins. The hyacinth and lima beans contain cyanogenic glycosides, which release cyanide when ingested. Several genera such as Derris (Tuba), Pachyrhizus (Jicama) and Lonchocarpus (Cube) are used as a fish poison and bio-insecticide. This is due to the presence of a toxic isoflavone called rotenone, which prevents cells from producing energy. Rotenone is also a potent cause of Parkinsonism, it damages dopaminergic neurons that control movement. The tonka bean (Dipteryx orodata) and sweet clover (Melilotus spp.) contain benzopyrone toxins called coumarins, which inhibit blood clotting. This causes massive internal bleeding and death. The life-saving but dangerous anticoagulant drug warfarin is developed from coumarin.

The alkaloid toxins of Fabaceae are just as diverse. They include the convulsant quinolizidine alkaloid cytisine of Laburnum,  indole alkaloid physostigmine of the Calabar bean (Physostigma venenosa), cardiotoxic diterpene alkaloid cassaine of the red water ordeal tree (Erythrophleum spp.), neurotoxic isoquinoline alkaloid erythraline of the coral tree (Erythrina spp.), and hepatotoxic (liver damaging) pyrrolizidine alkaloid monocrotaline of the rattlepods (Crotalaria spp.). Physostigmine has a nerve-gas like action which is exploited as paralytic in modern anaesthesia.

The most poisonous plant in the world belongs to Fabaceae, it is the rosary pea (Abrus precatorius). A. precatorius seed contains a deadly poisonous toxalbumin called abrin, which is about one order of magnitude more lethal than ricin!

Based on experimental toxicity (LD50) alone, the rosary pea (Abrus precatorius) is the most poisonous plant in the world.

Abrus precatorius, flower and immature seedpod.

The red water ordeal tree (Erythrophleum suaveolens) is infamous around Africa. Its bark exudes a red coloured liquid containing a deadly alkaloid called cassaine. The red-water trial by ordeal is still performed in Africa today.

The showy rattlepod (Crotalaria spectabilis) is native to Southeast Asia. It is rich in pyrrolizidine alkaloids, which cause massive liver damage and pulmonary hypertension.

The red coral tree (Erythrina fusca) contains a toxic alkaloid called erythraline, which causes muscle paralysis.

The Djengkol beans or Jering (Archidendron jiringa) is commonly consumed in Southeast Asia. It contains a toxic amino acid called djenkolic acid, which can cause kidney damage.

The Jicama or yam bean (Pachyrhizus erosus) is widely cultivated for its edible tuber. However Jicama seeds contain high concentration of rotenone. Ingestion of more than eight seeds is fatal to humans.

The Tuba root (Derris elliptica) is rich in rotenone. It is used by Southeast Asian tribesmen as fish poison. Tuba fishing causes massive destruction to aquatic ecosystem, it is outlawed but still conducted illegally. Derris powder was once marketed as an organic insectide, but it was discontinued due to health concerns.