How to tell male and female cannabis plants apart: differences and similarities
Learn to identify male and female cannabis plants
In short:
- Cannabis is a dioecious plant: there are male plants (which produce pollen), female plants (which produce the buds that are consumed) and monoecious plants (with flowers of both sexes on the same plant).
- The difference shows during flowering: the female has pistils with fine, white stigmas; the male, small ball-shaped pollen sacs. Before flowering, they can only be told apart with a genetic test.
- When growing, males and monoecious plants are removed to prevent pollination (seeded buds); feminised seeds give ~99.9% female plants.
Cannabis is a captivating plant for many reasons, but today we'll focus on its reproductive strategy. *Cannabis sativa *belongs to a small group of flowering plants that have male and female individuals; in other words, it is a dioecious plant. This dioecious trait of cannabis makes it possible to produce seedless buds with the potential for high concentrations of terpenes and cannabinoids such as CBD and THC.
Telling female plants from males, and the strains that can produce one sex, the other or both, has been essential for growers and breeders to increase the yields of their weed crops and improve their strains. In this post I explain the differences and how to tell male, female and monoecious (commonly known as hermaphrodite) cannabis plants apart.
Sexual reproduction in cannabis: why are there males and females?
Isn't it curious that there are male and female cannabis plants?
Well, I'll start by telling you that the fact that the Cannabis sativa plant has males, females and monoecious individuals was what most drew me to study it during the period of cannabis legalisation in Colorado, in 2013. My career as an evolutionary biologist and my PhD thesis are based on understanding why sexual reproduction exists in natural populations.
Cannabis: a dioecious and monoecious plant
Cannabis is a dioecious plant, which means that some individuals have male flowers and others have female flowers. Only 6% of flowering plants, known as angiosperms, show this type of sexual expression, among them cannabis (*Cannabis sativa *L.) [1,2]. The fact that cannabis is part of this minority of dioecious plants makes it even more intriguing.
Cannabis has male and female individuals, which in biology is called a dioecious plant. Only a minority (6%) of flowering plants (angiosperms) are dioecious.
Now, cannabis plants (and hemp plants too) also have monoecious individuals, which are those that produce both male and female flowers on the same plant. Although they are colloquially called hermaphrodites, that name is not correct, because hermaphrodite plants are those that have male and female reproductive organs in the same flower, whereas monoecious plants have male and female flowers on the same plant, but not necessarily in the same flower.
Differences between male and female cannabis: how to tell them apart
What is a male cannabis plant?
Male cannabis plants are those whose flowers produce pollen, and they are characterised by the presence of stamens and anthers (known as male or staminate flowers). Cannabis pollen is dispersed by the wind to pollinate female plants (anemophilous pollination).
How can you tell a female cannabis plant?
For their part, female cannabis plants are those that produce flowers with female organs, such as the pistil, where the stigmas are found; in cannabis these can vary in colour (female or pistillate flowers).
What is a monoecious cannabis plant?
Monoecious cannabis plants produce male and female flowers on the same plant; in other words, they produce both pollen and pistils with stigmas. These plants can self-fertilise and produce seeded buds, as well as pollinate other female plants around them. In a cannabis grow, monoecious plants are removed just as if they were male plants.
Apparently, according to anecdotal reports, these plants can also produce hermaphrodite flowers, known as “bananas” or “nanners” (“platanitos” in Spanish). Instead of producing male flowers, they just develop a stamen without sepals inside the female flower. This exposed stamen deposits pollen directly onto the buds, which allows self-fertilisation and guarantees successful pollination.
The monoecious phenotype, like all phenotypes, has a genetic basis, and some hemp plants are always monoecious, but this phenotype can also appear because of environmental influences, such as photoperiods and hormones, among other environmental conditions.
Cannabis pollination: buds with seeds!
The flowers of female cannabis plants have the highest number of trichomes (from the Greek for “hair”), small structures where cannabinoids such as CBD and THC are produced and concentrated. That is why, when we consume cannabis, it is the flower of the female plant that is used, also known as buds.
When a female plant is pollinated, it produces a type of dry fruit called an achene, which contains a single seed: this is what we know as a hemp seed.
In cannabis grows, you don't want the flowers to be pollinated, because you would end up with seeded buds. That's why growers work to spot and remove male and monoecious plants.
Although hemp seeds have plenty of nutritional properties, nobody likes finding them in their joint. That's why, when growing weed for smoking, it is common practice to spot male and monoecious plants and remove them to prevent pollination.
In fact, although cannabis can produce seeds, it isn't grown for seed or hemp oil, because its yield is low. For those uses, cannabis varieties with high seed yields are grown (grain hemp). For more information, see our post on the differences between hemp and cannabis.
What male and monoecious cannabis plants are useful for
In a cannabis grow, male and monoecious plants are always avoided, because the aim is for the flowers of the female plant not to be fertilised, so that they produce a greater amount of compounds such as cannabinoids and terpenes (these apparently decrease when pollination occurs). But also because nobody wants seeds in their joints, which is the commercial reason why pollination of female cannabis is avoided by removing male plants from grows.
Things are very different on industrial hemp farms (the same species, Cannabis sativa), where pollination is wanted in order to obtain seeds that are then used to produce food and oil.
Male cannabis plants are needed to create new crosses with diverse traits.
But note, when the aim is to improve or produce new strains, males are needed, and perhaps monoecious cannabis plants too, to obtain pollen for new crosses. You need to be very careful when working with pollen, so that you only pollinate the plants you want and no others.
How to tell male and female cannabis apart
Male and female cannabis plants look identical during the seedling stage and the start of vegetative growth, but they begin to differ as they progress into their flowering phase.
The differences between male and female cannabis lie in their flowers. Both female and male flowers develop at the nodes of the plant (where the branches meet the main stem), and you have to look at them closely to tell them apart. That way, you can distinguish male or female flower structures:
- Female cannabis plants show their sexual traits in the form of fine, elongated stigmas, white or sometimes purple.
- Male cannabis plants have no stigmas; instead they grow small pollen sacs, often in clusters. When these sacs open, they release their contents and pollinate the female plants, which apparently could reduce cannabinoid production because of the pollination. If you are growing cannabis, you should not let these plants reach that point. Fortunately, male and female plants can be told apart while the flowers are still immature and, using genetic tests before they flower.
When can you tell male cannabis from female?
Some people can tell female and male plants apart in early flowering. Pre-flowers are the first stage of flower development. They don't differentiate until a few weeks later, when they show their female or male traits and can be clearly told apart.
Male pre-flowers can be distinguished by their shape, like small eggs, rounder than female flowers, and, seen under a magnifying glass, completely smooth, with no hairs or trichomes.
Some also say that the distance between the stem nodes is greater in males than in females, and that for this reason they can be told apart even before flowering, but these are anecdotes with no scientific backing.
Why are there male, female and monoecious cannabis plants?
The reason why some plants, such as cannabis, have male, female and monoecious individuals is still unknown, but there are many scientific hypotheses that try to explain it. What we do know, though, is that, just like humans, male cannabis plants have a Y chromosome, in other words, they are XY. Also like humans, female cannabis plants have two X chromosomes, meaning XX.
Monoecious plants apparently have chromosomes very similar to those of females, XX, and the regions of the genome (the plant's DNA) that allow monoecious plants to produce both male and female flowers are not yet known.
Can cannabis change sex?
Now, to make things more complex, you may have heard of, or even tried yourself, what is known as sex reversal. This is when chemical compounds such as silver nitrate or colloidal silver are used on females so that they produce male flowers and pollen, or ethephon on males so that they produce female flowers. These compounds modulate ethylene, an important hormone in plant growth and development [3], either inhibiting it [4] or stimulating it [5].
Cannabis plants can produce flowers of the other sex, and this can be induced using feminising or masculinising agents.
Cannabis breeders and strain developers have been using the sex reversal technique to self-fertilise plants with desirable traits. This is why Cannabis sativa could be considered a plant with plastic or inconsistent sexual expression (plastic sex expression, also described as “leaky” or “inconsistent”), because its sex can be reversed with feminising or masculinising agents [6, 7] and also because males and females sometimes produce flowers of the opposite sex [8].
Feminised seeds: trying to guarantee female cannabis plants
As I told you above, the sex of *Cannabis sativa *plants can be reversed using chemical agents, and some strains even produce flowers of the opposite sex when they are under stress or because of changes in light or water. When a female plant is fertilised with its own pollen, or with pollen from a female that has undergone sex reversal and produced pollen, the seeds do not carry a Y chromosome (the chromosome of male plants). These seeds are known commercially as feminised seeds.
Feminised seeds lack the Y chromosome, so the plants have a minimal chance of producing pollen.
Feminised seeds have a high probability of growing into female cannabis plants. Most feminised cannabis seed banks offer a 99.9% guarantee of producing buds.
Two things: first, these feminised seeds *usually *produce only females, but occasionally males and monoecious plants turn up. Second, these feminised plants can also undergo sex reversal with chemical agents or when under stress, producing male flowers and pollen.
Open questions on sexual expression in cannabis
The possibility of sex reversal raises many questions. For example, where are these genes that are “switched on” or “switched off” when sex reversal happens? Are these genes on the sex chromosomes, or in other parts of the genome? Why are some cannabis strains more prone to sex reversal than others? Do they differ in the type of genes, or do they have the same genes but differ in how they are expressed? How much do genes control sexual expression, and how much is down to the environment? Why does this possibility of sex reversal, or this plastic or inconsistent expression, exist? Could it have some adaptive advantage? … Well, I could fill this whole article with more and more questions!
I hope you have found sex determination and sexual expression in Cannabis sativa as interesting as I do. Understanding how the different factors interact could allow growers to take advantage of this species' flexibility to modify its sexual expression. And, by using these techniques, offer farmers more efficient methods for getting a good harvest.
Keep learning about growing cannabis
References
1. Charlesworth D. What maintains male-sterility factors in plant populations? Heredity. 2002;89(6):408-409.
2. Renner SS, Ricklefs RE. Dioecy and its correlates in the flowering plants. Am J Bot. 1995;82(5):596-606.
3. Ecker JR. The ethylene signal transduction pathway in plants. Science. 1995;268(5211):667-675.
4. Kumar V, Parvatam G, Ravishankar GA. AgNO3: a potential regulator of ethylene activity and plant growth modulator. Electron J Biotechnol. 2009;12(2).
5. Yamasaki S, Fujii N, Takahashi H. Characterization of ethylene effects on sex determination in cucumber plants. Sex Plant Reprod. 2003;16(3):103-111.
6. Moliterni VMC, Cattivelli L, Ranalli P, Mandolino G. The sexual differentiation of Cannabis sativa L.: a morphological and molecular study. Euphytica. 2004;140(1-2):95-106.
7. Truta E, Gille E, Toth E, Maniu M. Some aspects of sex determinism in hemp. Anale Şt Univ "Al. I. Cuza" Iaşi, Genet Biol Mol. 2007;8(2).
8. Pannell JR. Plant sex determination. Curr Biol. 2017;27(5):R191-R197.
9. Mandolino G, Carboni A, Forapani S, Faeti V, Ranalli P. Identification of DNA markers linked to the male sex in dioecious hemp (Cannabis sativa L.). Theor Appl Genet. 1999;98(1):86-92.
10. Törjék O, et al. Novel male-specific molecular markers (MADC5, MADC6) in hemp. Euphytica. 2002;127(2):209-218.
Frequently asked questions about male and female cannabis
What is male cannabis used for?
Why males exist is a question Charles Darwin himself asked in “On the Origin of Species”, and it is one of the most beautiful questions in evolutionary biology. The short explanation is that males serve to provide genetic variation within populations. Male cannabis plants fertilise the females so that they produce diverse offspring.
What is female cannabis used for?
Female cannabis is where cannabis flower comes from: the part of the plant that contains the trichomes, the organs where cannabinoids such as THC or CBD are produced. It is what we commonly call buds. What we smoke, or what is processed to make CBD sweets, biscuits, brownies, etc., is the flower of the female plant.
When can you tell the sex of a cannabis plant?
With the naked eye, during flowering. Early detection, while they are still seedlings, is possible with genetic tests that detect the presence of the Y chromosome. Several companies offer this service using genetic markers. These markers tell you nothing about monoecious plants, nor about the chance that the plant will produce male flowers under stress or through sex reversal.
Can you buy female cannabis seeds?
Yes. In fact, many breeding companies have made these feminised seeds their flagship product.
Can you tell if a cannabis plant is male from its seeds?
Technically yes, but it is quite complex: you would find out with a DNA extraction, which is difficult to do on Cannabis sativa seeds. The most common approach is to detect male plants when they begin to develop their flowers.
What happens if a cannabis plant is male?
If you find a male plant in your grow and you are not going to do any breeding, the best thing is to remove it to stop it pollinating the females. The same goes for monoecious plants.
What part of a male cannabis plant is smoked?
Male plants are not usually smoked because they barely contain any cannabinoids. If the plant has a good structure or interesting traits, it can be used for crosses with the best females to obtain strains with the desired characteristics.
What happens if you smoke a male plant?
You will probably not feel any effect because of its low cannabinoid content. In addition, compared with the female's buds, the male has very low levels of terpenes, so its smell and aroma are weaker. As it matures it produces quite a lot of pollen, and many people are allergic to it.
What is the difference between male and female cannabis?
Male plants are identified by small balls in the axils of leaves or branches (the male flowers, which produce pollen as they mature). Females have pistils with stigmas that vary in colour, resembling tiny hairs.
How can you stop male and female cannabis plants from crossing?
By detecting male plants in time and removing them from the grow so that they do not pollinate the females.
What is hermaphrodite cannabis?
In reality there are no hermaphrodite cannabis plants (with male and female organs in the same flower). There are monoecious Cannabis sativa plants, where the plant has both male flowers and female flowers.
How does monoecious cannabis come about?
In some strains the monoecious traits can appear at any time, even in feminised seeds, due to stressful environmental factors such as a lack of water, nutrients or changes in light.
How can you tell whether cannabis has been pollinated?
Look at the flower and check whether the bracts have enlarged: these small leaf-shaped structures protect the female's reproductive organs. If you are suspicious, open the bracts with tweezers; if there is a seed inside, pollination occurred.
How do seeds form in cannabis buds?
If you find seeds in your bud, it means there was a male plant nearby in the grow, or a female that, under stress, started to produce pollen. The pollen travels on the wind and pollinates the female flowers, which then produce seeded buds. That is where the achene forms, a dry single-seeded fruit (the hemp seed).
Are there self-fertile cannabis plants?
Yes; Cannabis sativa can self-fertilise when it is monoecious or when there is sex reversal. Apparently, these self-fertilised plants degrade over a few generations, which in biology is called inbreeding depression.
The flowers we consume come from the female cannabis plant. Here is a selection of our CBD flower:
