Yes most plants ( not conifers)are build from three layers L1 L2 and L3 and those fit each other like a glove. They cannot be equated with cell layers, they are genetic entities. In monocots L1 forms the outer layer and a substantial part of the edge of the leaf ( see Sanseveria Laurentii with yellow edge) L2 also is often a single cell layer and forms the gametes, (pollen and eggs) ( not the L3!!). The L3 forms the bulk i.e. the inner part of a plant. The situation is different in dicots There L1 is colourless and the colored edge of the leaf is the L2 ( one gets only green seedlings from Hedera Gold herz). Lastly a somatic mutation is not necessarely confined to the outer layer L1. If it does one has a chimera ( A chimera is a plant were one or two layers of the three L1, L2, L3 are genetically different.