Anatomy of a cannabis plant
Developing an understanding of cannabis plant anatomy has two key benefits for growers.
First, it is of course much easier to maintain plant health, maximise produce and sustain high quality when armed with the knowledge of the function of each component of the plant.
Secondly, increased knowledge of cannabis plant anatomy will make growing a much more interactive and rewarding experience.
Cannabis plants are dioecious, meaning that they have male flowers (containing reproductive organs) on one plant and female flowers (also containing reproductive organs) on another plant within the same species. In short, the majority of cannabis plants are either male or female; rarely are they both (a hermaphrodite).
Male plants produce pollen sacs rather than flowers, though it is common to hear both male and female reproductive organs referred to as ‘flowers’.
On female plants, before the formation of the flower begins, pre-flowers (technically called primordium) develop at the points where the branches meet the stem. These sections are called nodes. Whereas male plants produce pollen sacs that hang in clusters, on female plants, preflowers produce the “calyx” which are designed to protect the plant’s reproductive organs.
Male “flowers” produce pollen, which when released, becomes airborne and fertilises female flowers. Once the female flower is fertilised it will produce seeds.
The flowers of the female plants produce the highest concentration of trichomes. These trichomes produce cannabinoids such as THC and CBD along with aromatic terpenes. As the female flower matures, the trichomes will change colour – starting life milky white, they will gradually become amber coloured.
In botanical terms cola is called “terminal bud”, though in common parlance it is more often referred to as the “bud site”. Cola grows only on female plants, and it is the part that looks like a tight cluster of bud.
The term cola refers to any group of flowers tightly growing together, but growers often use “cola” to refer only to the “apical bud” found at the top of the plant. Despite the focus usually being exclusively on the apical bud, cola also grows in smaller clusters among lower branches.
Cola is a complex component, containing the reproductive organs of the plant.
The word calyx comes from the Latin word ‘kalyx’ meaning ‘husk’ or ‘covering’. On female plants the calyx is actually the bud.
The calyx is the first part you see when the plant begins to flower. It simply looks like a collection of tiny leaves, usually in a teardrop shape, which then sits at the base of the flower, connecting it to the branch. Different strains of cannabis plant contain calyx of differing appearance in terms of colour, shape and size.
On female plants the calyx contains pistils, which in turn each contain two hairs. These hairs are called stigmas. In contrast, the calyx on the male flower contains no stigmas, but rather, produces pollen sacs that hang lower than the female equivalent. When the female plant is fertilised, the calyx forms a protective shell around the seed that will grow inside it. If however, the plant is not fertilised, the female calyx will contain the highest concentration of trichomes in the plant.
Cannabis plants originally developed trichomes as a means of protection from predators and adverse weather conditions. The resin they produce also works to glue pollen from male plants to the female flowers. Under a magnifying lens, trichomes resemble tiny silvery-white coloured mushrooms, but to the naked eye, trichomes are the layer of crystal resin that coats bud.
The resin produced by trichomes contains cannabinoids such as THC and CBD, as well as aromatic terpenes, although different strains of plant produce different degrees of these. Growers can maximise the production of cannabinoids and terpenes in their plants through careful genetic selection during the fertilisation process, alongside ensuring optimal soil quality and lighting.
There are two main types of trichomes: glandular and non-glandular. Glandular trichomes contain the resinous glands that produce THC and CBD, and these are usually found on the flowers and sugar leaves of the plant. Non-glandular trichomes on the other hand, appear to produce small hairs instead. These non-glandular trichomes are commonly found on the stem and fan leaves, though occasionally they can also be found on the flower.
When examining a plant, sugar leaves are the smaller, long thin leaves that grow closest to, or out of, the female flower. The role of sugar leaves is to photosynthesise and thus produce a source of localised energy for the flower itself.
Sugar leaves differ from fan leaves in content as well as appearance. They are resin-coated due to the fact that they contain a significant amount of trichomes.
The amount of sugar leaves present on a plant varies between strains. Some may contain very few, while others may develop colas that contain a high population of them.
The primary function of fan leaves is to conduct photosynthesis and thereby fuel the growth and reproduction processes of the plant. Growers can largely judge the health of their plants by examining fan leaves. Discolouration, wilting or curling of these leaves indicates a problem such as nutrient deficiency or imbalance in the water.
Fan leaves are a useful indicator of the primary strain of plant. Sativa strains tend to grow fan leaves containing nine fingers, while indica strains tend to grow leaves containing only seven fingers. It is commonly claimed that sativa strains of cannabis are more energising, whereas indica strains have a more relaxing effect. In reality, medical and other scientific research demonstrates that the distinction between effects is not quite that simple, being more reliant on chemical compounds rather than the sativa or indica origin.
Pistils are a primary component of the female plant’s reproductive organs and are located in the calyx. The pistils are elongated in shape and initially white in colour, and it is from these that the hairs, or “stigmas” emerge.
The role of the pistil is to capture pollen released from male plants. As the flower reaches reproductive maturity, the pistils change colour from white to amber, red or brown.
Contrary to popular belief, the colour of the pistil does not denote the quality of the cannabis. Pistils do not contain trichomes, and therefore contain no cannabinoids.
The term “node” refers to the part of the plant where the branch meets the stem. It is in the nodes where cannabis flowers form.
Different strains of plant have different proportions of nodes. Indica strains tend to produce more nodes, therefore making them bushier than plants of the sativa strain.
In contrast to nodes, “internodes” refers to the spacing between the areas where the branches connect to the stem.
The stem contains a vascular system that carries water and minerals from the roots to the plant’s extremities. Aside from this vital function, the stem also physically supports the structure and weight of the plant.
Growers will often deliberately prevent stems from growing too tall, usually cutting them short, or “topping” them, after the plant has developed around five vertical nodes.
This forces the plant to grow more laterally, thus becoming bushier and generating more bud sites.
Cannabis plants are inherently complicated, fascinating organisms that are too often overlooked. Becoming familiar with their biology and needs is essential for growers, but it will also help buyers distinguish between good and bad products.
For advice on how to identify good quality cannabis seeds, see our recent article on the subject. If however, you are more intrigued by the botanical and biological side of cannabis, we recommend our recent article on the anatomy of the cannabis seed, which illustrates the complexity of this plant even before it has become fully established.