Have you ever gazed in wonder at the deep purple hues within a cannabis flower and
wondered why some have such pigmented colours? Well you are not alone, and we are
here to dive into the phenomenon together. The short answer to the question “What
makes cannabis purple?” is Anthocyanins and/or Anthocyanidins, derived from two
Greek words: Anthos meaning flower, and Kyanos meaning blue.

Anthocyanins are an odourless subtype of naturally occurring flavonoids (more to
come on Flavonoids in future blogs). Anthocyanins contain colouring pigment and are
typically found in the epidermal layer of some plants, as well as certain cannabis
cultivars. Ranging in pigment and intensity, anthocyanins can appear in the leaves,
stems, roots, flowers, and fruits of plants. When the leaves change colours in the fall it
is partially due to a decrease in chlorophyll levels (green pigment) and the increase in
anthocyanins (blue, red, purple, red pigment) and carotene (yellow pigment) which
create that beautiful array of leaves the fall season is known for.

The intensity of colour that will manifest depends in part on the pH level during
growing, and in part on the environmental climate. Anthocyanins may be used as pH
indicators because their color changes with pH; they are red or pink in acidic conditions
(pH < 7), purple in neutral conditions (pH ≈ 7), greenish-yellow in alkaline conditions (pH
> 7), and colorless in very alkaline conditions, where the pigment is completely reduced.

Temperature also plays a vital role in the quantity of anthocyanins a plant will
accumulate. When the temperature cools, chlorophyll production goes down which
gives anthocyanins the perfect opportunity to shine and boost production. As a result,
the spectrum can range from deep shades of blue, black, purple, pink, or red giving
each plant its own unique artistic composition. Some examples of plants that contain
high levels of anthocyanins include blueberries, raspberries, cherries, tulips, red roses,
and many more. Purple Punch, Grandaddy Purple, Red Congolese, Stuffed French
Toast, and Blueberry are all classic cultivars that are known for having potentially high
levels of anthocyanins.

Anthocyanidins are the sugar-free counterpart to Anthocyanins. Anthocyanidins
are also widely consumed in the human diet, showing up most abundantly in red wine,
fruits, and some vegetables. The most common types of anthocyanidins are cyanidin,
delphinidin, pelargonidin, peonidin, petunidin, and malvidin. Don’t worry there won’t be a
quiz, but let’s skim over these funky sounding pigments.

In nature Cyanidin is a reddish-purple pigment. It is the major pigment in berries
and other reddish-coloured vegetables such as red sweet potato. Delphinidin is similar
to most of the other known anthocyanidins. It appears as a blue-reddish, or can even
produce purple pigment in the plant. The blue hue of flowers is due to the delphinidin
pigment. Pelargonidin differs from most of the anthocyanidins. In nature, it appears as red-colored pigment. Pelargonidin gives an orange hue to flowers and red to some of
the fruits and berries. Peonidin is another type of anthocyanidin abundantly found in
plants. It has the visible colour magenta. Peonidin is abundantly found in berries,
grapes, and red wines. Malvidin is another type of anthocyanidin. It has a purple colour,
and is plentiful in blue flowers. Malvidin is also the major red pigment in red wine. Last
but not least, there is Petunidin. It is a dark red or purple pigment that is soluble in
water. Petunidin has been detected in blackcurrants and purple petals of flowers.

At this point you might be wondering “Why do these pigments exist?” One reason is
species survival, for example in flowers the colouration may serve to attract pollinators,
while in fruits it may be beneficial in seed dispersal by attracting herbivorous animals to
potentially fruit-bearing plants. Furthermore, anthocyanins may have a protective role in
plants against extreme temperatures. One example of this is how tomato plants protect
against cold stress with anthocyanins. Whatever the reason, these little artists
(anthocyanins & anthocyanidins) work to create breathtaking colours. And potentially
even more exciting, they are also being studied for their potential health effects (Khoo et
al., 2017).

References:

Khoo, H. E., Azlan, A., Tang, S. T., & Lim, S. M. (2017). Anthocyanidins and anthocyanins: colored pigments as food, pharmaceutical ingredients, and the potential health benefits. Food & nutrition research, 61(1), 1361779.
https://doi.org/10.1080/16546628.2017.1361779