ggplot, add lines to create grid that will surround each bubble?

Question

I have a bubble plot that looks like this.

iris$group = c ( rep ( "A", 50), rep ( "C", 25), rep ( "D", 50) ,rep ( "E", 25) )

ggplot(iris,
       aes(x =  group, 
           y =  Species ,
           colour = Species ,
           size = Sepal.Width )) +
  geom_point() +
  labs(x = NULL, y = NULL) +
  theme(legend.position = "none",
        panel.background = element_blank(),
        panel.grid = element_blank(),
        axis.ticks = element_blank())  

this will create a bubble plot however what I really want is to have each bubble encased in a box. I drew the lines in read in the below picture. Is this possible? When I turn on the grid ,it usually just cuts into the circles.