Cannabis plant morphology
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Cannabis Plant Morphology: Growth Stages and Structural Features
Leaf Morphology and Developmental Progression
Cannabis sativa exhibits a dynamic progression in leaf morphology throughout its life cycle. Early leaves start with simple serrations, increasing in complexity to nine leaflets by the sixth true leaf, then gradually reducing in leaflet number as the plant matures. The peak leaf area is observed around the twelfth leaf, coinciding with a shift from opposite to alternate leaf arrangement (phyllotaxy). As the plant transitions from vegetative to reproductive phases, leaf complexity decreases, eventually producing single leaflet leaves at higher nodes. Stipule development at nodes 5 and 6 marks the vegetative phase, while bract and solitary flower development at nodes 7–12 signals the onset of the reproductive phase .
Inflorescence Structure and Florogenesis
The main product of medical cannabis is the female inflorescence, which is rich in glandular trichomes. Under long photoperiods, solitary flowers and bracts develop in shoot internodes, indicating that flower induction is likely age-dependent rather than photoperiod-dependent. Short photoperiods induce intense branching, resulting in a compound racemose inflorescence structure. Each inflorescence consists of condensed branchlets with reduced leaves, bracts, solitary flowers, and axillary shoots. This architectural change is crucial for maximizing productivity and uniformity in cannabis cultivation 61.
Trichome Development and Morphological Variation
Glandular trichomes, especially capitate stalked types, are abundant on female inflorescences and are the primary sites for cannabinoid and terpene production. Trichome density increases significantly after flowering begins, particularly on the abaxial (lower) surface of bracts. Trichome development, stalk length, and glandular head diameter are influenced by plant age and genotype, with asynchronous formation leading to varying stages of maturity on a single plant. Post-harvest handling and drying can also affect trichome morphology, potentially impacting cannabinoid content in the final product 1105.
Achene (Seed) Morphology and Domestication Effects
Cannabis achenes (commonly called seeds) show significant morphological variation depending on domestication purpose. Domesticated plants (hemp or marijuana) have longer, heavier achenes with less adherent perianth and lack pronounced basal attenuation compared to wild (ruderal) plants. Marijuana achenes are typically shorter and darker than hemp achenes, and fiber cultivars have larger achenes than oilseed cultivars. These differences reflect the "domestication syndrome" and are shaped by selection for specific uses .
Environmental Influences on Morphology
Light spectrum and photoperiod are key environmental factors affecting cannabis morphology. Different light sources (HPS, LED) and light spectra can alter plant height, flower dry weight, and cannabinoid content. For example, high-pressure sodium lights produce taller plants with more flower dry weight, while certain LED spectra can increase specific cannabinoid concentrations. The ratio of red to far-red light (R:FR) and the presence of short wavelength radiation (blue, UV-A, UV-B) can also influence plant height, inflorescence yield, and secondary metabolite accumulation 49.
Genotype, Phenotype, and Trait Correlations
While cannabis displays extensive variation in traits such as branching, leaf morphology, and cannabinoid content, these traits are not always genetically linked, especially in hybrid populations. This means that commonly used naming conventions based on leaf shape may not reliably indicate chemical properties, particularly in modern hybrids. Selection for vigorous growth, high stature, and wide inflorescences is expected to increase overall cannabinoid production, but trait correlations can be weak or absent in inter-crossed lineages 78.
Landrace and Historical Morphological Diversity
Historical landrace varieties, such as the Maghreb Landrace Kif, exhibit unique morphological traits that distinguish them from both European hemp and drug-type Cannabis indica. Key distinguishing features include the density of pistillate inflorescences and the density of capitate stalked glandular trichomes on perigonal bracts. These traits are useful for identifying and preserving traditional cannabis varieties .
Conclusion
Cannabis plant morphology is shaped by a complex interplay of genetic, developmental, and environmental factors. Leaf and inflorescence structures change throughout the plant’s life cycle, with trichome development and achene morphology reflecting both natural variation and domestication. Environmental conditions, especially light quality and photoperiod, can significantly influence plant architecture and secondary metabolite production. Understanding these morphological traits is essential for optimizing cultivation, breeding, and the identification of unique cannabis varieties for industrial, medicinal, and research purposes 1245+5 MORE.
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Morphological Characterization of Cannabis sativa L. Throughout Its Complete Life Cycle
Photoperiod-driven morphological changes in Cannabis sativa L. cv. White Widow occur throughout its life cycle, providing valuable insights for industrial and research applications.
The morphology of Cannabis sativa L. Achenes
Cannabis sativa L. achenes show significant divergence among domesticated plants, with hemp and marijuana achenes being longer, heavier, and less adherent, reflecting advantages from domestication for specific purposes.
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