But really, a few popular plants produce distinct gender differences; so here's how to
Eggplant- Apparently for these guys, males are better (fewer seeds/less bitter).
Check for maleness by the "belly button" on the bottom of the plant (opposite end from the stem): males have a smaller, more circular 'button' while females often have one in the shape of a line or slit. I was also told that males may be more bulbous shaped, as females are overall more tubular.
Fennel- Again, the male version is more desirable.
Male fennel plants are usually wider and more bulbous as well; females are more slender.
Asparagus- both genders are equally palatable! I just thought it was neat that there was in fact a difference between male and female asparagus.