The synthesis of many carbon nanomaterials is based on the ignition of carbon plasmas during laser ablation or arc discharge phenomena. This paper intends to compare these two methods in the formation of carbon nanotubes and linear carbon chains when a liquid phase is used as the environment for the plasma ignition. We observe similarities in the chemical species (mainly sp hybridized linear carbon chains) trapped in the liquid phase after the processes and we give also details on the properties of multiwall carbon nanotubes deposited at the cathode during arc procedures. It is found that these properties strictly depend on the discharge current and the electrode geometry. Particularly interesting is also the observed formation of tube-chain hybrids during unstable discharge conditions..