Strophanthus kombe

Strophanthus kombe
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
Order: Gentianales
Family: Apocynaceae
Genus: Strophanthus
Species: S. kombe
Binomial name
Strophanthus kombe
Oliver

Strophanthus kombe is a vine that grows in the tropical regions of Eastern Africa. It is part of the genus Strophanthus which contains approximately 38 species. S. kombe contains a cardiac glycoside which directly affects the heart. Historically both the seeds and roots of the plant were used in the preparation of the poison arrow head used for hunting. Today, the seeds are used pharmaceutically for patients with certain heart conditions that affect blood circulation. The plant has been used for two extremes; ending a life and saving a life so proper dosage is crucial when using this plant medicinally. The plant is not grown in large amounts. The seeds are traded primarily with Europe, but have been exported to the United States and Japan as well.

Distribution

Strophanthus kombe is found growing naturally in the tropical regions of southeast Africa. It is not a cultivated species and is usually seen growing as a wild plant. It is not typically seen growing in other regions although, cuttings are taken from the African plant in April to be potted and grown in the Royal Botanical Garden, Kew, United Kingdom.

Habitat and ecology

Strophanthus kombe is usually found on an isolated hill known as a monadnock near water sources such as coastal forests, gallery forests, riparian thickets and woodlands. They are able to grow at a range of altitudes starting at sea level and rising to 1100m above sea level. It is usually found in the forests between the coast and center of Africa as a vine. It is rarely seen growing in solitary but when it does it grows in bush form. It is a wood climbing vine that grows to the highest points on tall trees. It is seen curling on the ground and draping from tree to tree.

Morphology

Strophanthus kombe is a deciduous vine that under solitary conditions can be found as a shrub. It can grow up to 3.5 meters, with a stem that grows up to 10 cm in diameter. The bark is a reddish brown, with dark brown, grey or black lenticels. The roots are thick and fleshy. The papery leaves are simple, entire and found in opposite arrangement. The young leaves are exceptionally hairy on both sides but as they age the top of the leaves become smooth. One to twelve cream colored flowers can be found on the peduncle. They are narrowly ovate or linear and slightly unequal. The dichasial cyme inflorescence is on the terminal end of the plant.

Flowers and fruits

The flower of Strophanthus kombe, is an inflorescence, bisexual, fragrant flower. It is cream colored, yellow at the base with red spots and streaks inside. There is a thick layer of hair on the outside towards the top, while the inside of the flower has very few hairs. The stamen of the flower is found near the base of the corolla tube. The pistil contains a style a few millimeters long, with a ring like head surrounding a minuscule stigma. The fruit of the flower contains two follicles that narrow towards the apex and ends in a knob of various sizes. It has two thick and hard walled compartments containing many spindle shaped seeds.

Medicinal

Strophanthus kombe is known for its historical use as a source of arrow poison. Today it is used medicinally to treat heart failure: cardiac glycosides extracted from the seeds slow down the heart rate but increase the force and efficiency of the contractions (source 1). Some glycosides can also be found in the roots and flowers. A mixture of glycosides known as strophanthin-k is found in the seeds. It is a white crystalline powder that is water soluble and able to form into sugars under warm acidic conditions.

Precursors for a semi-synthetic compound known as acetylstrophanthidin, are found in the seeds of Strophanthus kombe. This compound, when used clinically, provides a rapid onset of vascular stimulant action.

Source 1 is Wink, Michael & van Wyk, Ben-Erik. (2008). Mind-Altering and Poisonous Plants of the World. Timber Press. London.

Trivia

This plant was inadvertently used as a medical experiment by Sir John Kirk, a nineteenth-century plant explorer who brought back specimens of Strophanthus kombe for the Royal Botanical Garden at Kew United Kingdom. Some of the plant’s juice accidentally got on his toothbrush. After brushing his teeth he reported a quick drop in his heart rate.

References