They were first used to denote the effective sex of plants (i.e. sex of individual in a given crossbreed, since most plants are hermaphroditic) by Carolus Linnaeus in 1751.
Another, perhaps more ancient, interpretation of these gender symbols names them as the spear for men and the distaff for women. A distaff (pronounced dih'-staf) is a weighted spinning tool on a string used for creating threads and yarns.
Numerous variations of gender symbols have been developed in the context of LGBT (lesbian, gay, bisexual and transgender) culture since the 1990s. Some of these symbols have been adopted into Unicode beginning with version 4.1 (2005).
From the symbol of Mercury (U+263F ☿). This symbol is used to indicate a virgin female (for example, in genetic analysis). Also used in botany to indicate flower with both male and female reproductive organs.