12. In a regular hexagon divided into 6 regions, as shown in Figure 1, the requirement is to plant the same type of plant in the same region, and different types of plants in adjacent regions. Given 4 different types of plants to choose from, there are $\qquad$ planting schemes.
12. 732

Consider $A, C, E$ planting the same type of plant, there are $4 \times 3 \times 3 \times 3=108$ methods. Consider $A, C,$ planting two types of plants, there are $3 \times 4 \times 3 \times 3 \times 2 \times 2=432$ methods. Consider $A, C, E$ planting three types of plants, there are $P_{4}^{3} \times 2 \times 2 \times 2=192$ methods. Therefore, the total number of methods is $108+432+192=732$.