Determining gender in some species of cacti has always been considered somewhat problematic. The Saguaro (Carnegiea gigantea) can be particularly challenging to both casual observers and seasoned researchers alike.
After many hours of careful observation in the field and researching the works of others I recently devised a nearly foolproof method for gender determination in (Carnegiea gigantea).
The results of that work are illustrated below.
Male
Female
Thanks to Cindy Collins for permission to use her photo of the female Saguaro.