Why Does Cannabis Turn Hermaphrodite?

Featured image: panel A cropped from Figure 3 in Punja & Holmes (2020), licensed under CC BY 4.0. Cropped to one panel; original panel label and scale bar retained.

A yellow anther appearing inside an otherwise female Cannabis flower is often called a “hermie” by growers and attributed to stress. Environmental conditions can contribute, but the appearance of male floral structures does not establish the cause on its own.

A plant can be genetically female and still produce male floral structures. Understanding this requires a distinction between genetic sex and floral sex expression, together with the influence of genotype, hormones and developmental stage.

Female chromosomes do not guarantee female-only flowers

Cannabis usually has an XX/XY sex-chromosome system, with XX plants genetically female and XY plants genetically male. The flowers a plant produces are more flexible than this chromosome distinction might suggest.

Researchers have repeatedly induced functional male flowers on XX plants without changing their sex chromosomes. The plant remains XX while its floral developmental programme changes. This capacity is described as sexual plasticity.

The role of ethylene

Plant hormones help regulate whether developing Cannabis flowers follow a male or female pathway. Ethylene is particularly important: higher signalling generally favours female flower development, while blocking ethylene perception can allow male flowers to develop on XX plants.

This response is deliberately used in feminized seed production. Increasing ethylene signalling can also promote female flower formation on genetically male plants. These responses show that hormonal regulation can alter floral expression without changing the underlying sex chromosomes.

Gibberellins and interacting hormonal pathways

Ethylene does not act in isolation. Gibberellins, or GAs, have long been associated with increased male flower formation in Cannabis. The transcriptomic work cited below reports substantial changes in genes involved in gibberellin metabolism during ethylene-driven sex reversal.

These findings support an interacting hormonal network rather than a single independent control. Changes in gene expression accompany the developmental response, but should not automatically be interpreted as proof that each altered gene causes sex reversal. More generally, plant signalling integrates multiple influences on development.

Different forms of male and female floral expression

Growers often use “hermie” for several distinct situations. A monoecious plant naturally produces separate male and female flowers on the same individual. An induced sex-reversed plant has been deliberately treated to develop flowers opposite to its usual genetic sex expression.

An otherwise female plant may instead produce a few exposed anthers within female inflorescences. These structures, often called “nanners”, are not necessarily equivalent to complete staminate flowers or clusters of male flowers. The Cannabis terminology work cited below describes this separately as antheral flowering.

The distinction matters when comparing an isolated anther late in flowering with extensive male flower development early in bloom. They differ in structure, timing and potential crop consequences, even though both may be described informally using the same word.

Genetic susceptibility

Cannabis lines differ in the stability of their sex expression. Some remain predominantly female across a range of conditions, while others more readily develop male floral structures. The cited reviews discuss differences in hormone production, sensitivity and expression of genes involved in sexual development.

Two plants in the same environment may therefore respond differently. Environmental conditions may contribute to the response, but the genotype influences susceptibility. Repeated expression in one cultivar does not establish an environmental cause on its own, nor does stability in another rule out an environmental contribution.

For breeders, this makes stable sex expression an important selection criterion alongside flower quality.

Environmental stress and male flower formation

Changes in photoperiod, temperature, water availability, nutrition and other environmental conditions have been associated with altered Cannabis sex expression. Controlled experiments defining precise, broadly applicable thresholds remain limited.

Claims that temperatures above 30°C always cause intersex flowers, or that one missed watering makes a female plant become male, are not justified as universal rules. A more useful working model is that environmental stress can influence hormonal and developmental signalling in a susceptible plant, with the response depending on genotype, developmental stage, treatment and severity.

This model helps interpret possible contributors without treating a visible anther as proof of one particular stress event.

Light leaks and interrupted nights

Photoperiod-sensitive Cannabis depends on night length to regulate flowering. Irregular lighting and interruptions of the dark period are therefore often considered when investigating unwanted floral development. The connection with photoperiodic signalling provides biological plausibility, but does not establish that any single light leak will cause intersex expression.

Responses depend on light intensity, timing, duration and genotype. Maintaining a stable dark period is sensible cultivation practice, while the explanation should remain more cautious than a universal light-leak rule. The article on flowering photoperiods and the switch to bloom discusses the separate question of how day length influences flowering.

Isolated anthers late in flowering

Growers sometimes find isolated yellow anthers very late in flowering. These may represent a different developmental situation from extensive early intersex expression. The morphology literature distinguishes antheral flowers from complete staminate flowers, including exposed anthers developing in older, senescing inflorescences.

Such anthers can potentially release pollen, so their late appearance does not make them irrelevant to the crop. However, one late anther is not sufficient evidence that the plant showed unstable sex expression throughout development. Timing, extent and floral structure should be recorded separately.

Floral expression changes without an XX-to-XY conversion

A stressed XX plant does not become XY because it develops male floral structures. Its sex chromosomes remain the same; the change concerns phenotypic expression.

Deliberate inhibition of ethylene signalling makes the distinction clear: an XX plant can form male flowers and produce pollen while remaining genetically female. Spontaneous intersex expression also reflects floral plasticity, but should not be assumed to have the same immediate cause as a breeder's controlled treatment.

Does feminized seed cause hermaphroditism?

Feminized seed production uses sexual plasticity, but this does not mean every feminized plant is inherently unstable. Parental selection matters. Repeated use of plants that readily develop spontaneous male flowers may perpetuate susceptibility, whereas selecting stable female parents and deliberately inducing pollen production does not by itself establish that offspring will become intersex.

Feminized status and spontaneous hermaphroditic expression therefore describe different things. Neither a seed label nor the fact that an XX parent produced pollen is sufficient to assess the offspring's stability under cultivation.

Why unwanted pollen matters

Pollination initiates seed development in receptive female flowers, which is undesirable in a crop intended to produce unseeded inflorescences. Research has confirmed that anthers formed within hermaphroditic Cannabis flowers can produce viable pollen and result in viable seeds. Even a small number of functional anthers can therefore matter in an enclosed growing area.

Early detection is useful, but finding the structure and identifying its cause are separate tasks. Removing an anther may prevent some pollination; it does not establish whether genetics, environment, development or their interaction caused its formation.

Interpreting the whole response

Unwanted male floral structures are best interpreted through the combination of genetic background, stability of sex expression, hormonal regulation, developmental stage and environment. A simple sequence from stress to hermaphroditism overlooks these interacting factors.

This also explains why plants can differ under similar conditions and why breeders can alter floral expression without changing sex chromosomes. Record when the structures appear, how extensive they are and what changed in the crop, while keeping the observed symptom separate from an unconfirmed explanation.

References

Richards, C.D., Ryu, B.-R., Gim, G.-J. & Park, S.-H. (2026). Hermaphroditism in Cannabis sativa L.: Impacts, Inducers, and Industry Implications. Plants, 15, 1643. https://doi.org/10.3390/plants15111643.

Roy, J., Monthony, A.S. & Torkamaneh, D. (2026). Gibberellin pathway remodeling accompanies ethylene-driven sex reversal in Cannabis sativa. Frontiers in Plant Science, 17, 1905836. https://doi.org/10.3389/fpls.2026.1905836.

Punja, Z.K. & Holmes, J.E. (2020). Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences — Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation. Frontiers in Plant Science, 11, 718. https://doi.org/10.3389/fpls.2020.00718.

Baek, K. & Vergara, D. (2025). A review of sexual strategies in Cannabis sativa L. under genomic and environmental controls. Agrosystems, Geosciences & Environment. https://doi.org/10.1002/agg2.70050.

Eckels, M., Heins, R. & Bugbee, B. (2026). Unraveling the Confusion of Flowering Types and Terminology in Cannabis sativa. HortScience. https://doi.org/10.21273/HORTSCI19059-25.