# Anthocyanin

> A water-soluble flavonoid pigment stored in cell vacuoles that colours leaves, stems and flowers red, purple or blue, set by genetics and enhanced by cool temperatures.

- Canonical: https://genetixbay.com/knowledge/glossary/anthocyanin.html
- Also written: anthocyanins, purple pigment, purple colour, purple color, purpling
- Glossary category: Plant biology · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Anthocyanins are flavonoid pigments made through the phenylpropanoid pathway and stored in the vacuole. Depending on the molecule and the vacuole's [pH](https://genetixbay.com/knowledge/glossary/ph.md) they appear red, purple or blue. In cannabis, whether a plant can turn purple is mainly genetic; cool temperatures, high light and late-season [chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md) breakdown bring it out (Bassolino et al. 2023).

## In practice

Purple bracts, [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) and stems in late flower are usually anthocyanin expression in a cultivar that carries it, often triggered by nights a good 5-10 °C (9-18 °F) cooler than days. A cultivar without the genetics won't purple however cold you run it.

Purple stems or petioles in veg are frequently genetic and harmless. They point to a problem only alongside other symptoms, such as dull, dark leaves with spotting (possible phosphorus or cold-root issues).

## Don't confuse with

- **Chlorophyll**: the green [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) pigment.
- **Carotenoids**: yellow and orange pigments revealed as chlorophyll fades.
- **Phosphorus deficiency**: may cause purpling, but with other leaf symptoms.

## Myth check

Cold for colour is real (Established). Claims that [cold nights](https://genetixbay.com/knowledge/glossary/cold-nights.md) add [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md), flavour or resin are unsupported unless peer-reviewed data shows otherwise; anthocyanin and yield have different temperature optima (Kim et al. 2025). Purple is [bag appeal](https://genetixbay.com/knowledge/glossary/bag-appeal.md), not potency. See [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md).

## Related terms

[Chlorophyll](https://genetixbay.com/knowledge/glossary/chlorophyll.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md), [Phytochrome](https://genetixbay.com/knowledge/glossary/phytochrome.md)

## Read more

- [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md)

## Sources

1. Bassolino L, Fulvio F, Pastore C, et al. 2023. When Cannabis sativa L. turns purple: biosynthesis and accumulation of anthocyanins. Antioxidants 12(7):1393. https://doi.org/10.3390/antiox12071393
2. Kim SR, Basnet P, Kovaleski AP, Ellison SL. 2025. Anthocyanin accumulation, inflorescence dry weight and total cannabidiol content have different temperature optima in Cannabis sativa. Journal of Cannabis Research 7:51. https://doi.org/10.1186/s42238-025-00311-w