In this paper, we study the multicast-capable routing , modulation and spectrum assignment (MC-RMSA) schemes that consider the physical impairments from both the transmission and light-splitting in elastic optical networks (EONs). Specifically, we propose to provision each multicast request with a light-forest which consists of one or more light-trees to avoid the dilemma that because of the accumulated physical impairments, a relatively large light-tree may have to use the lowest modulation-level and hence consume too many frequency slots (FS'). In order to further improve the spectral efficiency and compensate for the differential delays among the light-trees, we incorporate the rateless network coding (R-NC) in the multicast system. We first formulate an integer linear programming (ILP) model to solve the problem for static network planning. Then, we propose three time-efficient heuristics that leverage the set-cover problem and utilize layered auxiliary graphs. The simulation results indicate that in both the ILP and heuristics, the MC-RMSA with R-NC can achieve better performance on the maximum index of used FS' than that without. After that, we evaluate the heuristics in dynamic network provisioning. The results show that the MC-RMSA with R-NC can effectively improve the performance of all-optical multicast in EONs to reduce the blocking probability.