The trunk of the half-mens plant is protected from damage by thirsty animals thanks to a covering of long spines.
“The half-mens [Pachypodium namaquanum], growing in the same [Namib] desert, has reduced its leaves to one small bunch sprouting from the top of a pillar-like trunk bristling all over with ranks of long spines that must deter many a thirsty animal from gnawing it in search of liquid.” (Attenborough 1995:272)