The Great Dyke is a geological feature that spans 550 kilometers across Zimbabwe, running from northeast to southwest. This intrusion of ultramafic igneous rock, characterized by narrow ridges and hills, dates to 2.5 billion years. Economically important minerals associated with the Earth’s mantle, including chromite (processed into chromium) and platinum-group metals, are abundant and actively mined in the Great Dyke. The high concentrations of magnesium and nickel from this underlying rock generates serpentine soils.
The Great Dyke, and other serpentine-soil areas of the world, are fascinating places for botanists, as they often contain endemic species that are adapted specifically to dealing with the three challenges of these soils: low levels of nutrients (e.g., potassium and nitrogen); high concentrations of toxic metals; and high concentrations of magnesium which (though required in small amounts by plants) restricts calcium uptake in plants. Zimbabwe’s Great Dyke contains approximately twenty endemic species–these are taxa which have likely evolved specifically to handle the serpentine soils in this region. My (Daniel’s) understanding is that the species Convolvulus ocellatus is more broadly found across Africa, while var. plicinervius, is, as noted, one of those endemic taxa.
If you would like to see images of the plant in habitat, please see the first link.