I'd like to provide you with another solution, though it by default turns the list into a matrix:
mx1 <- do.call(rbind,list(c("A","O"),c("F","O"),c("F","O"),c("F","OP")))
mx1
[,1] [,2]
[1,] "A" "O"
[2,] "F" "O"
[3,] "F" "O"
[4,] "F" "OP"
mx1[,1]
[1] "A" "F" "F" "F"
mx1[,2]
[1] "O" "O" "O" "OP"