Seedsman Blog
Home » Shape And Size Of Cannabis Seeds May Indicate Cannabinoid Levels, Study Suggests

Shape And Size Of Cannabis Seeds May Indicate Cannabinoid Levels, Study Suggests

Many growers speculate about the relationship between cannabis seed appearance and the quality of the plants that they produce. Yet, most cultivators agree that little – if any – useful information can be gleaned simply by eyeballing seeds. However, a new study in the journal Cannabis and Cannabinoid Research suggests that the shape and size of cannabis seeds may, in fact, provide some clues as to the levels of THC and CBD in the resulting flowers[i].

Cannabis Seed Morphology And Cannabinoid Content

When we talk about cannabis seeds, we are actually referring to achenes.

Achenes are a type of non-fleshy fruit, each containing a single seed surrounded by a durable layer called a pericarp. Within this outer wall lies the embryo, which, if germinated, will produce a seedling.

To conduct their research, the authors of this latest study examined achenes from five different cannabis varieties. Two contained only THC, one contained only CBD, and the remaining two produced both cannabinoids. After examining the seeds from each of these cultivars, the researchers noted the “the achenes from the different chemotypes were clearly distinguishable.”

More specifically, they found that THC-only varieties tend to be larger and more rounded, with increasing CBD levels associated with smaller size and a more slender shape. Based on this analysis, they conclude that “achene shape variation is a potential biomarker of cannabinoid content in the plant flowers.”

Very little research into the significance of cannabis seed morphology was conducted before this study, with the only notable paper written way back in 1974. Appearing in the Canadian Journal of Botany, the study found that the achenes of domesticated weed plants are typically larger than those of wild varieties[ii]. The author even went as far as to speculate that ancient cultivators may have deliberately selected larger cannabis seeds when breeding plants, as these could be buried deeper to protect them from being eaten by birds. Should this be the case, we can thank these long-forgotten growers for the large cannabis seeds produced by modern plants.

So, Are Larger Cannabis Seeds More Potent?

Unfortunately, the results of this research can’t be considered a definitive guide to gauging cannabinoid levels. The study authors point out that “no significant differences between varieties from the same chemotype were observed.” In other words, it may be possible to discern between high and low-THC cultivars based on seed morphology, but when looking at two cannabis seeds from the same strain, size and shape suddenly become irrelevant.

This means that smaller achenes can contain more THC than larger specimens from the same cultivar. So, there’s basically no way of telling which of your cannabis seeds will produce the most potent plants.

While we’re on the subject, it’s worth mentioning that there’s also no way of reliably distinguishing male and female cannabis seeds. Some have suggested that female seeds are larger, yet the reality is that this simply isn’t the case. If it were, then there would have been no need to go to all the trouble of developing feminised seeds!

[i] Márquez F, Lozada M, Idaszkin YL, González-José R, Bigatti G. Cannabis Varieties Can Be Distinguished by Achene Shape Using Geometric Morphometrics. Cannabis and Cannabinoid Research. 2021 May 31. –

[ii] Small E. Morphological variation of achenes of Cannabis. Canadian Journal of Botany. 1975 May 15;53(10):978-87. –

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

This post is also available in: French

Ben Taub