Anatomy of a Cannabis Plant

Misnomers

The cannabis growing industry’s taxonomy and scientific/horticultural terminology have often differed in the past due to some long standing misunderstandings and mis-terminology. With these varying definitions/understandings of anatomical terms, we can only do our best to make sense out of what is often a plethora of conflicting information. For example, the term “calyx-to-leaf ratio” is already embedded in growing culture and it’s doubtful that the more accurate “bract-to-leaf ratio” will replace it any time soon. But thanks to industry awareness, and the recent exponential growth of peer reviewed research, everyone has a more accurate understanding of the relationships between, and terminology of, the various parts of the cannabis plant.

Cannabis is Dioecious

Cannabis is dioecious, meaning the male and female reproductive organs are on different plants. Female plants are the targets of commercial cultivation due the presence of pistillate flowers, which are key to the production of glandular trichomes. Glandular trichomes produce and contain the bulk of a plant’s cannabinoids and terpenes and are thus the commercially targeted product of the cannabis plant. The male cannabis plant does not grow flowers in the same way as female plants do; Males only produce pollen sacs and therefore produce very low levels of cannabinoids and terpenes.

Here is an outline of the key anatomical structures of the cannabis plant:

Trichomes

Trichomes are microscopic resinous structures formed primarily on pistillate (female) cannabis flower surfaces, particularly concentrated on bracts. These pointed, bulbous, or stalk-like appendages come in various types and perform very important functions such as affecting leaf temperature, facilitating photosynthesis, pest-deterrence, ensuring less palatability to animals, and the production of the key cannabinoid and terpenoid components of cannabis (as well as a complex array of secondary metabolites).

Cannabis has six kinds of trichomes: three are non-glandular and three are glandular (resin-bearing). Only glandular trichomes produce cannabinoids and these can be separated into three categories: bulbous trichomes, capitate-sessile trichomes, and capitate-stalked trichomes.

Indumentum

The indumentum is the velvety covering of trichomes on the surface of a cannabis plant, particularly proximate to mature flowers and colas. The indumentum is the glistening, white “frosting” which has led to a lot of related terminology such as the “sugar” in sugar leaves.

Inflorescence

A collective term for the entire floral structure of the cannabis plant.

Pistillate Flowers (Female)

The pistillate flower is the female cannabis plant’s inflorescence. A cannabis pistillate flower is made up of the ovule with its protective perianth and two stigmas enclosed by glandular-trichome-producing bracts. Pistillate flowers are rich in trichomes.

Staminate Flowers (Male)

Staminate flowers are the male cannabis plant’s inflorescence. Males do not produce pistillate flowers and therefore have very low levels of cannabinoids and terpenes. Male plants instead produce small round flowers formed of five tepals (small protective leaf-like petals) these tepals protect five anthers which produce pollen. These staminate flowers are often referred to as pollen sacs.

Bracts

Bracts and bracteoles are small teardrop-shaped leaf structures which enclose and protect the ovule, the perianth, and the stigmas.

Bracts are teardrop-shaped leaf-like structures that overlap in small, tight whorls to form the outermost part of the female cannabis flower. They act as a covering and protection for the more fragile parts of the flower. The surfaces of these bracts are the area of primary glandular trichome formation and hold the highest concentrations of cannabinoids and terpenes. Cannabis growers often incorrectly refer to bracts as calyxes.

Calyx and Perianth

The female calyx cells are part of a delicate, translucent layer of tissue that partially encloses and protects the ovule called the perianth. Each female pistillate flower has a single ovule with its protective perianth and a pair of stigmas, which is then itself encapsulated by leaf-like bracts.

Bracts are commonly misidentified as calyxes. The calyx is not visible (inside the flower) while Bracts are easily identified. If a seed were to form through pollination, the perianth would form the seed’s protective encasement.

Ovule

The central reproductive portion of the cannabis pistillate flower. The ovule can form a seed when pollinated.

Stigmas

Stigmas are the fine, hair-like structures that emerge from the bracts . Each pistillate flower has two stigmas that protrude from a single ovule, which is covered by the calyx and enclosed by the bracts. A stigma’s primary role is that of pollen catcher. They range in a wide variety of colours from white to pale yellow and they darken to red and orange as the plant matures. The colours of stigma help to judge the maturity and ripeness of cannabis flowers. They are also the first sign to look for in a developing plant to determine sex. Growers often refer to stigmas as “pistils”.

Stigmatic Papillae

The increasingly tinier hair-like structures that cover the surface of the hair-like Stigmas which grow from pistillate flowers. Stigmatic Papillae catch male pollen out of the air.

Colas

colas are the collective clusters of flowers that form at the end of a branch or the top of the stalk on a female cannabis plant. Colas are the targeted/harvested portion of the plant and contain the highest concentrations of the key glandular trichomes formed primarily on the bracts.

Sugar Leaves

These are the smaller, triangular, trichome-covered leaves proximate to, or within, the colas. Although they are technically leaves and not part of the flower, sugar leaves can contain useful amounts of cannabinoids from the trichomes on their surface.

Fan Leaves

Fan leaves are the large and broad leaves of the plant. Fan leaves are the photosynthetic factories of the cannabis plant, capturing light and producing sugar. Fan leaves also serve to provide shade and temperature control via aspiration. Fan leaves do not form a large amount glandular trichomes on their surface.

Rachis

The five cannabis leaf leaflets join together at the point known as the rachis. The rachis attach to the stalk or branch by a leaf-stem known as the petiole.

Petioles

The foot and stem portion of the cannabis plant leaf. Varying in colour and size dependent upon strain, its length connects the rachis, where the leaflets come together to form a leaf, with the stalk or lateral branch.

Nodes

Nodes are the bulges where joints form on the stalk of a cannabis plant. Nodes are the growth point for lateral leaf and stem growth. Various cannabis species have differing internodal spacing. Nodes are one of the parts of the cannabis plant where most growth happens and most hormones are produced

Stipule

The small, narrow spear-like leaf growing at each node is called the stipule,

Stalk

The stalk of a female cannabis plant is the main stem from which branches, leaves, pistillate flowers, and colas grow. It contains the vascular system which works to carry moisture and nutrients from the roots to the leaves via xylem cells, and to transport the sugars and starches produced via photosynthesis around the plant for use or storage via the phloem cells. Phloem is otherwise known as bast, the part of the cannabis or hemp plant that is traditionally harvested for fiber to make rope, canvas etc.

Roots

The roots of the cannabis plant are found below ground and serve to anchor the plant to the earth while providing a pathway for the uptake of water and nutrients. The roots also store carbohydrates for use in other functions of the plant.