Short answer. Cannabis (Cannabis sativa L., family Cannabaceae, which it shares with hops) is an annual, wind-pollinated herb. Plants are either male or female (dioecious), with sex set by X and Y chromosomes; that separation has been stable for millennia, and intersex ("hermie") plants are unwanted outliers, mostly from poor breeding (see male, female and hermaphrodite plants). The resin that growers value (cannabinoids such as THCA and CBDA, plus terpenes) is made in glandular trichomes, which are densest on the bracts of unpollinated female flower heads.
What's happening
Cannabis grows fast in long days, then switches to flowering when nights get long (photoperiod types) or after a fixed age (autoflowering types). The flowering switch is less "turning on flowers" than a change in shoot architecture: the growing tips stop making long internodes and start building the compact, branched flower clusters we call colas [2].
The genome is diploid with 2n = 20 chromosomes: nine pairs of autosomes plus the sex chromosomes (XX female, XY male) [3]. The genes that decide THC versus CBD sit in large, repeat-rich, low-recombination regions, which is why chemotype tends to be inherited as a block (see chemotype inheritance) [4].
Taxonomy is argued over. Most botanists today treat cannabis as one species, Cannabis sativa, with subspecies and varieties; the familiar "sativa / indica / ruderalis" labels are a separate, popular vocabulary that does not map cleanly onto genetics (Contested; see indica, sativa and ruderalis) [1][5].
The parts
| Part | What it is | Why a grower cares |
|---|---|---|
| Taproot and fibrous roots | Primary root plus a dense lateral mass | Root-zone health limits everything above it |
| Stem and nodes | Hollow-ish stem; leaves and branches arise at nodes | Node spacing (internode length) shows light and genetics |
| Fan leaves | Palmately compound leaves, usually 5-9 serrated leaflets (1-3 on seedlings and late flower) | Main photosynthetic surface; first place deficiencies show |
| Sugar leaves | Small, resin-coated leaves inside flower clusters | Trimmed at harvest; trichome-rich |
| Stipules and pre-flowers | Small structures at nodes; the first solitary flowers form here | First visual sign of sex [2] |
| Female flower | A single ovary wrapped in a bract (often called "calyx" by growers) with two stigmas ("pistils", "hairs") | Bracts carry most glandular trichomes; stigmas catch pollen |
| Male flower | Five tepals and five anthers hanging on short stalks | Sheds pollen about 1-3 weeks after opening; one plant can seed a room |
| Glandular trichomes | Capitate-stalked "mushroom" glands, plus smaller sessile and bulbous types | Where cannabinoids and terpenes are made and stored |
| Seed (achene) | Single seed in a hard shell, mottled or plain | Carries half its genes from each parent |
Where the resin is made
Cannabinoids are made as acids (THCA, CBDA, CBGA) inside the secretory cells of glandular trichomes and pushed into the head's storage cavity. They become neutral THC or CBD mainly by heat (decarboxylation), not on the living plant (Established) [1]. Unpollinated female flowers keep building bracts and resin for longer, which is why drug-type crops are grown seedless (sinsemilla).
Numbers that matter
| Parameter | Typical value | Notes |
|---|---|---|
| Chromosome number | 2n = 20 (18 autosomes + XX or XY) | [3] |
| Haploid genome size | ~818 Mb (female) / ~843 Mb (male) | Flow cytometry estimatesbeing reviewed |
| Leaflets per fan leaf | 5-9 mature | 1-3 on first true leaves and at the top in flower |
| Height outdoors | 1-5 m (3-16 ft) | Strongly genotype and season dependent |
| Life cycle | 3-9 months seed to harvest | See life cycle |
Common mistakes
- Calling the stigma the "pistil" and assuming its colour tells you ripeness. Stigma browning is a rough cue; trichome maturity is the better one.
- Assuming "sativa" and "indica" describe genetic ancestry. In modern hybrids they mostly describe shape and expected effect (Contested).
- Thinking male plants contain no cannabinoids. Males make resin too, just far less flower mass.
Evidence
- Dioecy with XY sex determination and 2n = 20: Established [3].
- Trichome localisation of cannabinoid synthesis: Established [1].
- Photoperiod response mainly reshapes the shoot apex rather than starting flowers from zero: Supported (one detailed study on three medical cultivars) [2].
- Single-species treatment: Supported but debated [1][5].
