APOCYNACEAE

The Apocynaceae or dogbane (and milkweed) family comprises some 5000+ species of trees, shrubs, climbers, or succulents, which are distributed across the tropics to temperate regions and deserts of the world. They are recognised for having waxy opposite leaves, showy contorted flowers, abundant latex, and fruits in the shape of paired berries, drupes, or long follicles containing winged seeds. Many Apocynaceae species are cultivated as ornamental plants, including the allamanda, periwinkle and oleander. 

 

Apocynaceae harbours some of the most deadly and medicinal plants known to humans. Principle toxins include the cardenolide glycosides and various indole alkaloids with neurotoxic or cytotoxic effects. The cardenolide glycosides prevent human body from regulating crucial ions flow, a process that is vital to the heart function. Victims poisoned by cardenolide glycosides can rapidly develop heart rhythm abnormalities and die. Hundreds of thousands of human deaths were attributed to the red-eyed sea mango (Cerbera manghas) and its congener Cerbera odollam due to murder, suicide and trial by ordeal-poison. Similarly, the seed of the yellow oleander (Cascabela thevetia) is a popular choice of suicide in parts of Asia, accounting for hundreds of deaths annually. Aboriginal African tribes exploit the cardenolide rich latex of various Acokanthera, Pachypodium and Strophanthus spp. as arrow poison to hunt large animals. Some Apocynaceae cardenolides like ouabain and thevetin were once used as heart medication, but  abandoned due to their unpredictable effects. Cardenolide glycosides show promise as anti-cancer agents in recent years. 

 

The indole alkaloids vincristine and vinblastine of the Madagascar periwinkle are successful developed into anti-cancer drugs, indicated for the treatment of leukemia and lung cancer. Other Apocynaceae indole alkaloids such as ajmalicine, reserpine and yohimbine are used as anti-hypertensive, anti-depressive, and as a drug to treat erectile dysfunction, respectively. The indole alkaloid ibogaine of Tabernaemontana spp. is taken as  ritual psychedelic (hallucinogen), it has the potential to treat addiction caused by drugs of abuse. 

 

The toxicity of Apocynaceae has driven some remarkable co-evolution with insect herbivores, especially butterflies of the Monarch family. There’s even a rodent that exploits Apocynaceae toxins. The African maned rat has learnt to chew on the bark of Acokanthera spp. and smear the toxins on its hair, which it raises as warning to  predators.

 

Subfamily Rauvolfioideae 

Red eye sea mango (Cerbera manghas)

The red eye sea mango is the most deadly plant known to humans. Its seeds were once used as an ordeal poison called Tangena, which was responsible for  hundreds of thousands of deaths in the past.

Yellow eye sea mango (Cerbera odollam)

 

Often used in murder and suicide, half of a Cerbera seed kernel is fatal to humans. The cardiac glycoside toxin cerberin is hard to detect by forensic scientists, hence nicknamed the 'perfect poison'.

Yellow oleander (Cascabela thevetia), yellow flower variant

Yellow oleander (Cascabela thevetia), orange flower variant

Yellow oleander (Cascabela thevetia), close up of flowers

 

 

A single Cascabela seed  is fatal to humans. C. thevetia is responsible for hundreds of suicide deaths in India and Sri-Lanka. It is one of the most deadly plants known to humans.

The Madagascar periwinkle (Catharanthus roseus) is widely cultivated by the pharmaceutical industry to produce two valuable cancer chemotherapy drugs, vincristine and vinblastine.

Catharanthus roseus, white flower variety.

Catharanthus roseus, pink flower variety

The Eve's apple (Tabernaemontana dichotoma) is said to induce hallucinogenic effects akin to the Datura. This is probably due to the presence of ibogaine-type indole alkaloid toxins.

Kopsia arborea 

The grape-like fruit of Kopsia arborea probably inspired its common name, the Penang Sloe. Sloe means a bluish black fruit. This species is rich in indole alkaloids, consumption is most unwise!

The rosy Kopsia (Kopsia rosea) is a common ornamental plant of tropical gardens.

Leuconotis eugenifolia is found in the secondary forests of Peninsular Malaysia. It exudes a thick sticky latex that was once used to make rubber. The plant is rich in indole alkaloids such as yohimbine.

 

The Frangipani (Plumeria rubra) is widely cultivated as a tropical ornamental plant.

Subfamily Apocynea

 

Nerium oleander horticulture cultivar 'Luteum Plenum'.

Nerium oleander 'Luteum Plenum' is a horticulture cultivar with orange-yellow flowers.

Nerium oleander single red flower horticulture cultivar.

Nerium oleander single pink flower horticulture cultivar.

Nerium oleander double pink flower horticulture cultivar. N. oleander is widely planted as an ornamental plant. It likely originates from the Mediterranean. Oleander is indeed highly poisonous, but the toxicity is greatly exaggerated by media. Oleander barely causes human deaths today.

The desert rose (Adenium obesum) is closely related to Nerium oleander, thus equally poisonous. Various horticulture cultivars of Adenium are highly coveted ornamental bonsai plants.

The Kudu lily (Pachypodium saundersii) lives in arid deserts of Africa. It has evolved into a succulent to conserve water. Aboriginal tribes use its highly poisonous latex as arrow poison. 

Pachypodium saundersii, close up of flowers.

The climbing oleander (Strophantus gratus) contains a potent cardenolide glycoside called ouabain in its seeds. It is widely used by hunters of Africa to make arrow poisons.

The tassel vine (Strophanthus preussii) is also used in parts of Africa as a component of arrow poison.

Rocket trumpet (Mandevilla sanderi), unknown toxicity.

Herald's trumpet (Beaumontia grandiflora), unknown toxicity.

Wrightia dubia, native to northern Peninsular Malaysia, unknown toxicity.

Subfamily Asclepiadoideae (milkweeds)

The Mexican butterfly milkweed (Asclepias curassavica) is a cultivated for its showy flowers, and as a host plant of the Monarch butterfly. This species exudes latex rich in cardenolide glycosides like asclepin, calotropin, uzarigenin. The latexi is known to cause severe eye injury.

Asclepias curassavica, close up of flower.

Balloon milkweed (Gomphocarpus physocarpus)

The curious looking seedpod of Gomphocarpus physocarpus has led to its common name, the balloon milkweed. Similar to A. curassavica, this species produces toxic latex which causes severe eye injury.

Giant milkweed (Calotropis gigantea), white flower variant.

Giant milkweed (Calotropis gigantea), purple flower variant. This species contains a highly potent cardenolide glycoside called calotropin, which is more toxic than strychnine. It is the preferred host plant of the plain tiger butterfly.

Seedpod of Calotropis gigantea.

The fragrant flowers of the Tonkin jasmine (Telosma cordata) are sometimes eaten as a vegetable in Southeast Asia. Its toxicity is currently unknown to science.

Heterostemma piperifolium is a herbaceous climber native to tropical Southeast Asia. This species is rich in alkaloids, but little is known about its phytochemistry.

Subfamily Periplocoideae

The rubber vine (Cryptostegia madagascariensis) is a hardwood climber that is native to Madagascar. It is an invasive species that damages local ecosystem and poison livestock in Australia. All parts of C. madagascariensis contain cardenolide glycosides.

Cryptostegia madagascariensis, flower cluster. Note: white leaf midrib and petiole.

Cryptostegia madagascariensis, immature flower bud.

Cryptostegia grandiflora is closely related to C. madagascariensis. It can be distinguished from the latter by its purple/pinkish petiole and leaf midrib.

 

Cryptostegia grandiflora, close up of flower.

Streptocaulon juventas is native to tropical Southeast Asia. The root of S. juventas is rich in cardenolide glycosides, which are investigated as anti-cancer agents.