Stenocereus Eruca
Stenocereus Eruca is certainly one of the most unusual cactus around. It is popular known as the 'Creeping Devil', and not without reason.
This a plant which grows prostrate on the ground, rooting as it goes along, with only top ends rising above the surface.

It can grow to over three metres long, but usually it is much less, as it breaks up to form shorter plants. Its yellow flowers about ten centimetres wide, and are produced during the night. Its dagger like spines are conspicuous, and deadly. The Creeping Devil is best admired at a distance.
Stenocereus Eruca