RUBIACEAE

The Rubiaceae or coffee family comprises approximately 13,000+ species of trees, shrubs and herbs of cosmopolitan distribution. It is closely related to the Apocynaceae, Gelsemiaceae and Loganiaceae, forming the order Gentianales. Rubiaceae exhibit opposite leaves with interpetiolar stipules, flowers borne in a cluster (cymose) and fruits in the shape of berries. Classical species include the coffee plant (Coffea spp.) and  cinchona tree (Cinchona spp.), both are cultivated for two alkaloids of economic importance, namely, caffeine and quinine. Caffeine is a purine alkaloid that produces mild stimulant effect, it is currently the most endorsed drug of ‘abuse’. Caffeine is indeed addictive, but it does not cause harm to the society. Caffeine toxicity causes uncontrolled trembling, panic attack and seizure. Meanwhile, quinine is a quinoline alkaloid which kills malaria and certain parasites. It imparts a bitter taste to tonic water. Quinine works by preventing malaria parasite from digesting red blood cells. However, it is quite toxic and can cause heart damage in overdose. Many synthetic derivatives of quinine like chloroquine and mefloquine are used in modern medicine to treat and prevent malaria.

Other Rubiaceae like Psychotria spp., particularly P. viridis elaborate tryptamine alkaloids like N,N-dimethyltryptamine (DMT), which is a hallucinogen. DMT is the active ingredient of the South American entheogen, Ayahuasca, which brings life changing enlightenment to users. Ayahusaca is made of a mixture of P. viridis and plants containing harmala alkaloids. The components are inactive if taken individually, but synergise to produce powerful hallucinogenic effects. It remains a mystery as to how ancient tribesmen discovered the effects of Ayahuasca. In Southeast Asia, another psychoactive Rubiaceae plant is the Kratom (Mitragyna speciosa). It contains indole alkaloids called mitragynines, which are somewhat similar in action to morphine. Mitragynines induce  stimulant and euphoric effect, followed by sensory depression with increasing dosage. Addiction and death due to Kratom is rare, but the species is considered as an illegal drug of abuse by some Southeast Asian countries.

Another genus of alkaloid producing Rubiaceae is the Ophiorrhiza (snake-root) of South Asia. Ophiorrhiza spp. are rich in quinoline alkaloids of the camptothecin skeleton. Camptothecin is a potent cytotoxic drug which kills dividing cells by inhibiting the uncoiling of DNA double-helix structure. Derivatives of camptothecin such as irinotecan and topotecan are used in modern medicine as anti-cancer chemotherapy drugs.

The most poisonous members Rubiaceae belong to the genera Fadogia and Palicourea, both are implicated in massive loss of livestock. In South Africa, Fadogia homblei causes a cattle disease called gousiekte, which is characterised by fatal heart damage. It is linked to pavettamine, a polyamine toxin produced by symbiotic bacteria living inside the F. homblei. The South American Palicourea marcgravii causes outbreaks of cattle deaths. It contains a toxin called fluoroacetate, which inhibits cells from using energy. Poisoned animals develop symptoms such as limping, respiratory weakness and death following physical exertion. There is no antidote available. Cattle poisoning due to P. marcgravii often results from massive deforestation, which causes domestic animals to consume unfamiliar plants. 

Kratom or Ketum (Mitragyna speciosa), flower.

Mitragyna speciosa, foliage.

Mitragyna speciosa, young leaf. Note: prominent interpetiolar stipules (a small leaf-like structure located on the stem, and in between the opposite leaf).

Ophiorrhiza sp., specimen from Penang, Northern Peninsular Malaysia. The genus Ophiorrhiza is diverse, similar looking species are difficult to identify.

Ophiorrhiza sp., seedpod.  Note: Miniscule brown seeds exhibiting vivipary (germination inside the seedpod).

Ophiorrhiza sp., growth form. This species prefers riparian habitat.