The Marijuana Plant Anatomy: Know the Complex Beauty of Weed

You may smoke weed. You may vape or dab. You may enjoy edibles. And you certainly know what an iconic marijuana leaf looks like.

If you don’t grow your own supply, though, you may not know very much about the marijuana plant.

That’s OK. It’s not necessary to know all about a cow’s anatomy to eat steak, either. But it certainly helps if you find yourself trying to decide between three similar-sounding cuts of beef like top round, tip round, and bottom round.

In the same way, it can’t hurt to know more about the marijuana plant than just “I love getting high.”

We’re here to help.

The History of the Marijuana Plant

It’s no secret that cannabis has been around a lot longer than Snoop Dogg, Willie Nelson, and the Woodstock generation of the 1960s. Weed use was prevalent during the Jazz Era of the earlier 20th century, too.

But you have to go back much further than that to discover the first recorded evidence of the marijuana plant. In fact, you have to go back about 12,000 years. That’s when cannabis was first grown in East Asia, according to evidence uncovered by archaeologists.

If you’re having trouble picturing when that was, it was during the Neolithic period at the end of the Stone Age. That’s right, weed dates back to the period when agriculture was first developed. There’s evidence of its use as a psychoactive drug in prehistoric Africa and Eurasia as well.

Marijuana use became more popular over the following millennia, and eventually became documented.

Traces of THC content were found in a 3,000-year-old mummy found in Egypt. The Greek historian Herodotus described communal baths with cannabis steam during the latter days of Ancient Greece, and there are credible reports of weed use in China, Central Asia, and the Middle East over the following 500 years.

In later centuries the cannabis plant made it to Africa, modern Europe, and eventually to America, carried by traders during the era of imperialism. Hemp was commonly grown in the U.S. during colonial days. But the custom of recreational marijuana use was brought to America by immigrants from Mexico, who arrived in the early 20th century during the Mexican Revolution.

Weed was made illegal nationwide in 1937 — and you know the rest of that story. However, the marijuana plant was here to stay and was it cultivated illegally until the start of the legalization era.

Types of Marijuana Plants

Cannabis is a genus in the small family of flowering plants known as Cannabaceae.

There are approximately 170 species and 11 genera in the family, including the Humulus plants that produce the hops used to make beer. Cannabaceae plants stand erect or climb, and are characterized by dry, one-seed fruits and flowers with no petals.

Hemp and marijuana are both cannabis plants, and they’re essentially the same. Their only important difference is that hemp produces just a minuscule amount of the psychoactive cannabinoid THC. Marijuana, of course, contains much more.

There are three species of marijuana: sativa (C. sativa), indica (C. indica) and ruderalis (C. ruderalis), although many classify ruderalis as a subspecies of sativa. The latter contains low levels of THC and is primarily used for its genetics by cultivators. That’s because it is an autoflowering strain that produces buds on a regular schedule, rather than being triggered by climate cues.

Most modern marijuana strains are hybrids, crossbred to contain qualities of both sativa and indica strains. That makes sativa and indica the two species worth learning more about.

Cannabis Sativa Plants

Sativa plants are believed to have first grown in East Asia, which is why they thrive in climates located between the Tropic of Cancer and the Equator with temperate or tropical climates. Those climates better accommodate sativa’s typically-long flowering period.

These marijuana plants grow tall and lanky, as high as 10-12 feet high. Their foliage is often sparse, with long and thin fan leaves that have between seven and 13 serrated lobes. They’re known to produce smaller harvestable yields than indica plants.

Sativa plants generally produce buds with greater THC content than indicas, and their effects are more likely to be euphoric, uplifting and/or cerebral.

Cannabis Indica Plants

Botanists believe that Indica plants originated either in Afghanistan or on the Asian subcontinent. They can tolerate somewhat colder climates and shorter growing seasons since they take much less time to flower.

These plants are more compact than sativa, often growing no taller than 4-5 feet. They’re bushier with more vegetation, denser buds, and broad fan leaves that usually feature only seven lobes.

Indica plants are known for producing flowers with somewhat lower THC content, whose effects are commonly more relaxing and sedating than sativa’s.

The Growth Stages of Marijuana Plants

Cannabis plants usually take anywhere from ten to 28 weeks to progress from seed to harvest. Their growth period is primarily dependent on whether they are sativa or indica plants, and on their specific strain.

Marijuana plants go through four distinct growth stages.

1. Germination: During their first stage of growth, the plants sprout and grow a few very small leaves (called cotyledon leaves). That’s followed by the emergence of tiny fan leaves.
2. Seedling: Fan leaves continue to emerge with an increasing number of “blades” on each set of leaves. Once the leaves have five or seven blades, growth accelerates.
3. Vegetative: Most of the marijuana plant’s growth occurs during this stage. It becomes large and hardy, and almost all of the plant’s fan leaves emerge.
4. Flowering: Pre-flowers develop toward the top of the plant, and then buds emerge and grow. In the second half of this stage, the sticky trichomes containing cannabinoids and terpenes proliferate until it’s time for harvesting.

Anatomy of the Marijuana Plant

Needless to say, marijuana plants grow from seed and spread roots in their growth medium. We’ll focus on the parts of the plant that can be seen above ground.

Stem, Nodes, and Branches

The large stem grows upright and supports the plant. It’s divided by nodes, from which branches emerge and grow. When a plant is young, the nodes and angular, furrowed branches develop in pairs on opposite sides of the stem. As it matures, the nodes emerge in an alternating pattern, first on one side of the plant and then on the other.

The vascular system inside these parts of the plant transport nutrients and water from the roots, and the energy that is generated via photosynthesis.

Fan leaves

The large leaves on a marijuana plant grow from the branches and capture the light needed for photosynthesis. They contain very few cannabinoids and terpenes.

Marijuana’s fan leaves are green and palmate (meaning lobes extend from their center, as fingers extend from the palm). They are coarsely serrated.

Mature leaves typically have 7-9 lobes; the longer and thinner leaves on sativa plants may have as many as 13 lobes, while wider indica leaves are more likely to have 7. The number of lobes depends on the plant’s genetics, although smaller numbers of lobes may indicate either environmental stress or re-vegetation.

Cannabis plants grow compound leaves, meaning they have multiple leaflets. The leaves are normally “opposite decussate,” with each set emerging an opposite pair that grows at a right angle to the last pair. The leaves may start to appear in an alternate pattern during the plant’s flowering stage.

Colas and Buds (Flowers)

The flowers on a cannabis plant don’t look like those on most flowering plants. The inflorescences grow on long, leafy stems that emerge from leaf axils.

Female flowers are paired, sessile buds that grow in tight clusters called colas, Most grow toward the top of the plant, although a few may emerge around lower nodes. Small sugar leaves grow out of the colas as well.

Inside the buds are bracts, tiny leaf-life structures which protect the plant’s reproductive parts. Two small stigmas (they look like hairs) protrude from each bract and are responsible for catching pollen from male plants. There is a single ellipsoid seed, usually brown and mottled, with a hard shell that’s covered by the ovary wall.

Male flowers look like small balls on sticks, with five hairy sepals and five large stamens. They grow in several areas of the plant and contain pollen. These flowers have virtually no cannabinoids or terpenes.

Trichomes

Trichomes are the small resin glands that emerge on buds during the flowering stage; they secrete the sticky resin that contains the bulk of a marijuana plant’s cannabinoids, terpenes and flavonoids. The trichomes are the “pay dirt” on a weed plant.

Marijuana Plant: FAQ

Q: How do you tell the difference between male and female marijuana plants?
A: You look at the “pre-flowers.” Male plants develop pollen sacs 4-6 weeks into the growth process. They can be seen at the nodes of the plant, and look like the small ball on a stick that we’ve mentioned. Female plants, by contrast, will have small bracts that eventually develop two stigmas. Most growers “sex” their plants and remove males from the grow as soon as possible; males don’t produce harvestable bud, and pollinated females are much less productive.

Q: Is it better to grow marijuana plants from seed, or from clones?
A: Both have advantages and disadvantages. Seeds are pest-free and disease-free, there are enormous numbers of sources for purchasing your desired strain, seeds develop into sturdier plants because they grow strong taproots, and it’s satisfying to see plants develop from seed. Clones grow faster, they’re less expensive, you know exactly what you’ll be getting — and you can be sure that you have female plants.

Reference

Ren, G., Zhang, X., Li, Y., Ridout, K., Serrano-Serrano, M. L., Yang, Y., … & Fumagalli, L. (2021). Large-scale whole-genome resequencing unravels the domestication history of Cannabis sativa. Science advances, 7(29), eabg2286. [1]