Crassula tetragona gets its specific name of tetragona from the leaf arrangement on the stems, botanically called its phyllotaxis. Plants with opposite leaf pairs succeeding each other in a perpendicular manner like those of C. tetragona are said to have decussate phyllotaxis.
The leaves of the species are also quite variable: cylindrical or sometimes flat, but still succulent. They may be from 1 cm to 5 cm long, usually incurved and up to 5 mm in diameter tapering to sharpish tips. Leaf colour may be grey, green or pinkish red as in this photo taken near Touwsrivier (Vlok and Schutte-Vlok, 2010; Wikipedia).