A re-evaluation of Haumaniastrum species as geobotanical indicators of copper and cobalt

The taxonomy and morphology of the ''copper flowers'' Haumaniastrum katangense and H. robertii are described. Herbarium collections are an important resource for evaluating potential geobotanical indicators of mineralization. Specimens collected from Angola, Zaire, Zambia, and Tanzania were analyzed for cobalt, copper, and zinc. Though both species are known to hyperaccumulate copper and/or cobalt (> 1000 mu g/g [ppm] in dried tissues), this ability appeared to be confined to specimens from the Shaban Copper Are in Zaare and adjacent parts of the Zambian Copperbelt such as at Solwezi. The reputation of H. katangense as a universal indicator of copper was not confirmed by the study as this showed the occurrence of several specimens over non-mineralized ground in Angola, Zambia and Tanzania. There is some evidence that H. katangense is a species present over disturbed ground where there is less competition from other plants. This intolerance of competition helps to explain the occurrence of this plant over phytotoxic mineralization. Despite its distribution both on and off copper-rich soils, the species still has value as a geobotanical indicator of copper/cobalt mineralization, particularly in the Shaban Copper Are. With one exception, there was no unusual accumulation of zinc in either species, probably because the copper ores of Central Africa are not particularly enriched in this element.