Plants come in both male and female genders, but the marijuana plant that we consume is always a female plant.
Cannabis is a dioecious plant, meaning different varieties have either male or female reproductive organs. Female plants can be grown with males present if you’re aiming for cross-pollination and new genetics. Otherwise, they can be grown in isolation, which would result in sensimilla — large buds devoid of seeds. Either way, all the resinous bud that’s consumed as marijuana comes from female plants.
While esoteric, it’s not impossible for laypeople to distinguish male from female plants. You can start by looking at the plant’s nodes — where the branch meets the stem. Pre-flowers occupy the nodes and are one of the defining factors in telling male from female. A male pre-flower looks like a tiny round ball, while a female pre-flower looks almost the same, but has thin hairs or “stigma” peeking out of it. About a month into the grow cycle is when you’ll be able to notice the pre-flowers and determine their gender.
If you want your female plants to grow big and strong, remove the males from the garden as soon as possible — as in, as soon as you can tell that they’re male.
While both the male and female plants are equally important for the diversity and longevity of the species, female plants can exist without males. If you only want female plants, you can guarantee this by getting clones or feminized seeds.