Euphorbia keithii old main stem

The lower, main stem of Euphorbia keithii loses side-branches and turns pale brown, rough and smooth patches seen all over. The old surface becomes thick and corky, bulging irregularly in places, dented in others, like barren land on a lifeless planet.

The vertical channels down the trunk lie parallel as beds of once strong-flowing rivers. The occasional crater-like wound is present where one of the last, large branches had been attached long ago.

Instead of always growing one erect stem only, a few big branches may last laterally, each ending in a separate rounded dome, a green cluster of small stem-tips. Each such dome continually loses its lowest branches, and thereby the outer tips on the outside of the dome. This leaves an elongating bare stem section below, and height increase by the emergence of new, central, green branchlets (Coates Palgrave, 2002; iNaturalist).