Electroconvection is studied in systems of different symmetry classes. Particular emphasis is laid on the onset behavior (threshold voltage and critical wavevector) of the patterns. The standard hydrodynamic description of nematics predicts regimes of stripe patterns (rolls) in five different wavenumber ranges for different combinations of the dielectric and conductivity anisotropies and the boundary conditions (planar or homeotropic director alignment), among them a new, isotropic variant. The novelty of that system is a direct transition to zig-zag modulated rolls and squares. On the basis of the rigorous analysis of the underlying nemato-hydrodynamic equations a suitable Swift-Hohenberg model has been constructed which gave a good quantitative reproduction of the observations in general and in particular explained the unusual, stationary, long-wave-modulated quasi-periodic square pattern.
Experiments have revealed two additional pattern types which are not captured by the standard model.