Although we all know what it is, you may have never stopped to analyze the parts of the cannabis plant and how important each of its functions can be for understanding where its effects come from.
All of this can affect the quality of the marijuana, among other things. Or if we want to buy from an online seed bank and start growing our own plant, it wouldn't hurt to do a thorough review to have a solid understanding of cannabis anatomy and morphology. This way, we can analyze it to understand how it works and get better results.
Cannabis (Cannabis sativa L.) is a complex taxon with variable morphological characteristics that growers must know in order to distinguish between varieties, recognize the stages of the growth cycle, and evaluate plant health.
The Seed and the Root
Marijuana seeds are like a small warehouse of elements and nutrients, ready to be germinated and begin taking root.
Each seed contains within it the complete genetic blueprint that will determine all subsequent production of cannabinoids and terpenes. Its internal structure includes a hard protective coat, cotyledons, a radicle (the embryonic root), primary leaves, and a growth apex.
If we bring together the right conditions of temperature, humidity, and oxygen, the seed will begin to absorb the surrounding water and swell until it opens. The first thing to emerge is the radicle, which will become the main or taproot, followed by the cotyledons — the first smooth, rounded leaves, distinct from the serrated leaves that will appear later.
The plant's root acts as the heart of a living system: it collects water, oxygen, and mineral nutrients from the substrate and sends them to the rest of the plant through its vascular system. According to botanical studies, the cannabis taproot can penetrate up to 30 cm deep, while lateral roots spread between 20 and 100 cm. In peaty soils, lateral roots are more developed and the taproot is limited to 10–20 cm.
As the plant grows, an extensive network of white or cream-colored secondary roots forms. Root health is directly linked to the overall health of the plant: it is important that the small white filaments (root hairs) do not dry out or turn brown, as this would indicate dehydration or possible rot problems.
Although not genetically part of the plant, mycorrhizae deserve a mention: these fungi form a mutually beneficial symbiotic relationship with cannabis roots (as they do with up to 90% of plant species), greatly expanding nutrient absorption capacity.
Stem and Branches
The main stem is the skeleton of the plant, its backbone. Botanically, the cannabis stem is green, hollow, cylindrical, and longitudinally grooved, with a woody interior that can be hollow at the internodes.
All information, water, and nutrients flow through it thanks to two differentiated vascular tissue systems that function like a two-way highway:
- Xylem: transports water and minerals from the roots upward, to the leaves and flowers.
- Phloem: distributes the sugars and nutrients produced by photosynthesis from the leaves to the rest of the plant, including roots, branches, and developing flowers.
Together, these two systems keep the plant fed and hydrated. Stems and branches are composed mainly of plant cellulose and calcium.
From the stem grow the branches, which together with it form the complete structure of the plant. Depending on genetics and training techniques, the plant will have more or less lateral branching, which explains why some varieties are wider and bushier while others have a Christmas tree shape.
It is important for the stem to grow healthy and strong because it must support the entire weight of the plant with its leaves and buds. In the early stages of growth the stem is flexible, but as the plant matures it becomes thicker and more rigid. Thicker stems are generally associated with better overall vigor and a greater capacity to support abundant harvests.
The Nodes
The nodes are the points where the stem and branches meet. They are key indicators of the plant's sex, as the preflowers, bracts, and sexual structures that allow identification of male or female plants appear at the nodes. The distance between nodes (internodes) also influences cannabinoid distribution and helps predict yield.
The Leaves
The leaf is one of the main protagonists of the plant. Beyond being the iconic symbol of marijuana, leaves carry the great responsibility of photosynthesis, a vital process in every plant. As primary photosynthetic organs, their morphology — size, shape, and structure — directly influences the plant's ability to capture light, exchange gases, and regulate transpiration.
The iconic cannabis leaves are palmately compound with elongated segments and serrated edges, typically composed of 5 to 7 unequal lobes, though they can have anywhere from 5 to 13 leaflets. They usually grow in pairs (opposite arrangement) and allow us to distinguish cannabis types by their shape and color:
- Indica – Characterized by wider leaves with about 7 broad leaflets and a darker green color.
- Sativa – In this case, the leaves are narrower, can have up to 9 or more thin leaflets, and display a lighter green color.
- Ruderalis – Produces small leaves with only 5 leaflets, two of which are much smaller and located near the base.
- Hybrid – A mix of the above, with intermediate characteristics.
However, recent studies (2022) have shown that plants identified as "indica" or "sativa" based on physical characteristics such as height or leaf shape are not, in fact, reliably chemically distinguishable. Many classified as "sativa" exhibit cannabinoid profiles typical of "indica" plants and vice versa. This suggests that the most relevant differences lie in the chemotype (chemical composition) rather than in visible morphology.
Experienced growers use fan leaves as health indicators: discoloration, wilting, or curling can signal nutrient deficiencies, over- or under-watering, or environmental stress.
Types of Leaves and Parts of the Cannabis Leaf
There are two main types of leaves on the cannabis plant:
- Fan leaves: The large, emblematic leaves, primarily responsible for photosynthesis. They can reach the size of a hand or larger.
- Sugar leaves: The small leaves that grow among the buds, covered in trichomes that give them a "sugary" appearance. They contain a significant concentration of cannabinoids and terpenes and are highly valued for making concentrates, hash, and extracts.
Each leaf, in turn, consists of several parts:
- Vascular System: distributes all the nutrients sent by the root through the veins.
- Sheath: Connects the stem to the petiole.
- Petiole: The stalk or base of the leaf that connects it to the branch. It transports nutrients and allows the leaf to orient itself toward the light.
- Rachis: In compound leaves, it is the continuation of the petiole from which the leaflets are distributed.
- Leaflet: Each of the separate pieces that emerge from the rachis — what we might call each "mini-leaf" of the compound leaf. A leaf can have from 5 to 13 leaflets, though 7 to 9 is most common.
- Upper surface (adaxial surface): The top face of the leaf, oriented toward the sun, absorbing its light and converting it into energy through photosynthesis.
- Underside (abaxial surface): The bottom face of the leaf, the one in the shade, where the stomata are found — the microscopic structures responsible for managing gas exchange of CO₂ and oxygen, as well as regulating transpiration.
NOTE: Leaves in the shade also serve a purpose — don't remove them indiscriminately! Although they are not as productive as those directly exposed to light, they still contribute to photosynthesis and energy storage. Defoliation (selective removal of leaves) is a common practice, but it should be done thoughtfully: to improve airflow, increase light exposure to the buds, and reduce the risk of mold — without weakening the plant.
The Flower
Here we arrive at the most prized part of the plant: the fruit of cultivation, whether for therapeutic or recreational purposes. Cannabis is a dioecious species, meaning it produces male and female flowers on separate plants, although modern genetics and stress can also give rise to hermaphrodite plants with both reproductive organs on the same plant.
The cannabis flower is wind-pollinated (anemophilous pollination). Flowers form at the nodes of the stems and branches, and will allow us to differentiate between male and female.
Complete guide to identifying male and female cannabis plants. Learn how to detect sex before flowering, avoid pollination and maximise your sinsemilla harvest.
FEMALE
This is the most interesting for the grower, as it is the one that generates the highest concentration of cannabinoids, including THC and CBD. Female structures consistently contain higher concentrations of compounds than male plants or other parts of the plant.
Female flowers are composed of several key structures:
- Cola: The dense cluster of flowers grouped at the top of the plant (apical cola) or at the ends of the branches.
- Bracts: Small teardrop-shaped leaves densely covered in trichomes that form a protective cover over the seeds. They are the part of the plant with the highest cannabinoid concentration, exceeding the rest of the flower's average by 15–20%.
- Calyx: A translucent layer that surrounds the ovule of the female plant at the base of the node, enclosed within the bract and not visible to the naked eye.
- Pistils and stigmas: Pistils are the female reproductive organs, from which the stigmas protrude — the "little hairs" responsible for capturing pollen from the male. The stigmas change color during flowering as the bud matures, going from white to orange and finally to red/brown, which is one of the indicators of maturity.
MALE
Male plants produce stamens with pollen sacs (anthers) supported by thin filaments that develop at the nodes. Once mature, these sacs open and release pollen into the wind with the intention of fertilizing the female flowers. They do not produce resinous buds when they flower and generate a significantly lower concentration of cannabinoids.
It is worth noting that, contrary to popular belief, studies by Dayanandan and Kaufman (1976) demonstrated that male cannabis plants produce similar amounts of glandular trichomes to females and present the same types of trichomes, albeit with lower cannabinoid production.
HERMAPHRODITES
In addition to males and females, cannabis plants can develop both reproductive organs on the same specimen. This is usually caused by environmental stress (sudden light changes, extreme temperatures, physical damage) or unstable genetics. Regular inspection during flowering, especially around the nodes and lower branches, is essential to detect and remove these structures in time and avoid unwanted pollination.
Why do some cannabis plants become hermaphrodites? Learn what causes it, how it affects your crop, how to avoid it, and which genetics are more or less stable.
Trichomes
Although tiny and almost invisible to the naked eye, trichomes are possibly the most important component of the cannabis plant for the consumer and patient. They are small, mushroom-shaped resinous glands that cover the buds, sugar leaves, and even the stems. Trichomes house approximately 95% of the plant's cannabinoids and terpenes, making them true "cellular microfactories" of metabolites.
Types of Glandular Trichomes
Science has identified three main types of glandular trichomes in cannabis, originally classified by Hammond and Mahlberg in 1973 using scanning electron microscopy:
- Bulbous: The smallest (10–15 μm), composed of only a few cells. They are distributed uniformly across the plant's surface but their contribution to resin is marginal and they do not produce cannabinoids or terpenes in any significant amount.
- Capitate-sessile: Larger and more abundant than bulbous trichomes, mushroom-shaped with a very short stalk that keeps them close to the epidermis. Found mainly on the underside of leaves and on young flowers. They produce cannabinoids throughout the plant's life cycle, but at lower levels than capitate-stalked trichomes. They have exactly 8 secretory cells in the disc.
- Capitate-stalked: The largest and the only ones visible to the naked eye. They have a prominent globular head on an elevated multicellular stalk. They are the primary source of cannabinoid and terpene production in flowering cannabis, with 12–16 secretory cells in the disc and a larger subcuticular cavity for storing resin.
A particularly interesting recent discovery is that sessile trichomes may actually be an earlier developmental stage of immature stalked trichomes, which changes our understanding of resin maturation.
Not everything that glitters is potent. Only pedunculated glandular trichomes (with "stick") produce THC/CBD. Look for milky-amber heads, not just glitter.
Biosynthesis and Maturation
In the trichomes, the disc secretory cells synthesize secondary metabolites: cannabinoids, terpenes, and flavonoids. It is important to know that the fresh plant contains mainly THCA and CBDA (acidic forms), which are converted into THC and CBD through decarboxylation during drying, curing, or combustion. The key enzymes in this process — THCA synthase and CBDA synthase — are located specifically in the capitate trichomes.
Trichome maturation is one of the most reliable indicators for determining the optimal harvest time:
- Clear/transparent: The plant is still immature.
- Milky/opaque: Optimal biosynthesis point, maximum cannabinoid concentration.
- Amber: Indicates the onset of degradation, with conversion of THC into CBN (more sedating).
Why Does the Plant Produce Trichomes?
Beyond their interest to the grower, trichomes serve natural defense functions: they act as a physical barrier against insects, protect against UV radiation damage, and produce chemical compounds that deter herbivores.
Why Avoid Pollination?
Unpollinated flowers will continue creating new calyxes and bracts, layer upon layer, and the bud will keep growing and fattening. Since the female plant wants to reproduce, it will generate more and more trichomes so that any pollen that may fall gets trapped in the sticky resin.
If pollination occurs, the plant will dedicate its energy to producing seeds instead of resin, resulting in buds with lower potency. That is why, to achieve maximum cannabinoid and terpene output, we must identify and remove male plants before they release their pollen, ensuring that the female flowers remain unfertilized (sinsemilla) and continue accumulating the resin that produces the effects we seek.
The density, size, and distribution of trichomes vary between varieties and are influenced by both genetics and growing conditions (UV light, nutrition, temperature, humidity). These morphological variations can affect the final concentration of active compounds by up to 40%.
Sources:
- Tanney, C., Backer, R., Geitmann, A. & Smith, D. L. Cannabis Glandular Trichomes: A Cellular Metabolite Factory. Frontiers in Plant Science (2021). Link
- Livingston, S. J. et al. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal (2020). Link
- Conneely, L. J. et al. Glandular trichome development, morphology, and maturation in high THC-containing cannabis inflorescences. Journal of Cannabis Research (2023). Link
- Emerald Harvest. Cannabis Plant Morphology. Link
- ScienceDirect. Trichome. Link
- Terpene Belt Farms. The Anatomy of the Cannabis Plant. Link