The stems are green and photosynthetic , and distinctive in being hollow , jointed and ridged -LRB- with sometimes NUMBER@1 but usually NUMBER@2 ridges -RRB- .

The stems are green and photosynthetic , also distinctive in being hollow , jointed , and ridged -LRB- with -LRB- NUMBER@1 - -RRB- NUMBER@2 ridges -RRB- .
