A recent botanical reclassification split off some species formerly in Senecio, putting the giant groundsels in the new genus Dendrosenecio.

It also redefined the former species Senecio cottonii, as a subspecies of Dendrosenecio johnstonii.

The giant grounsels of the genus Dendrosenecio evolved, about a million years ago, from a Senecio that established itself on Mount Kilimanjaro, with those that survived adapting into Dendrosenecio kilimanjari.

As it moved down the mountain, the adaptations necessary for the new environment created the new species, Dendrosenecio johnstonii.

[2] Dendrosenecio johnstonii can be up to 10 meters tall, and grow to 40 centimeters (17 inches) or more in diameter.