Remove 'a' from legend when using aesthetics and geom_text

How can I can remove the letter 'a' from the legend generated by this code? If I remove the geom_text, then the 'a' letter will not show in the legend. I want to keep geom_text, though.

ggplot(data = iris, aes(x = Sepal.Length, y=Sepal.Width, 
                        shape = Species, colour = Species)) + 
   geom_point() + 
   geom_text(aes(label = Species))

Set show.legend = FALSE in geom_text:

ggplot(data = iris,
       aes(x = Sepal.Length, y = Sepal.Width, colour = Species,
           shape = Species, label = Species)) + 
    geom_point() +
    geom_text(show.legend = FALSE)

The argument show_guide changed name to show.legend in ggplot2 2.0.0 (see release news).

Pre-ggplot2 2.0.0:

With show_guide = FALSE like so...

ggplot(data = iris, aes(x = Sepal.Length, y = Sepal.Width , colour = Species,
                        shape = Species, label = Species ), size = 20) + 
geom_point() +
geom_text(show_guide  = FALSE)