Cannabis leaf morphology
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Cannabis Leaf Morphology: Developmental Patterns and Genetic Regulation
Leaf Morphology Progression in Cannabis sativa
Cannabis sativa exhibits a dynamic progression in leaf morphology throughout its life cycle. Early in development, the first true leaves display simple serrations, and as the plant matures, the number of leaflets per leaf increases, reaching up to nine in the sixth true leaves. After this peak, the number of leaflets gradually decreases, with mature plants sometimes producing leaves with only a single leaflet at higher nodes. The leaf area also peaks around the twelfth leaf, which coincides with a shift from opposite to alternate leaf arrangement (phyllotaxy) Hesami2023Hesami2024.
Genetic Control of Leaf Morphogenesis
The development of cannabis leaf morphology is tightly regulated by specific genes. During the transition from simple to compound leaves, genes such as YAB, AGO5, and TCP4 are upregulated, indicating their role in leaflet formation and overall leaf structure. The transition from vegetative to reproductive phases is marked by changes in gene expression, particularly in genes like SPLs, ELFs, SOC1, and CEN-Like, which are associated with flowering and phase transition .
Photoperiod and Phase Transition Effects
Photoperiod, or the length of day and night, significantly influences cannabis leaf morphology. The shift from vegetative to reproductive growth is marked by the development of stipules at specific nodes and the emergence of bracts and solitary flowers. Short-day photoperiods trigger the formation of apical inflorescences and further changes in leaf complexity and structure Hesami2023Hesami2024.
Leaf Morphology and Trichome Development
While the iconic cannabis leaf is well recognized, it is the flowers that are most valued for their cannabinoid and terpene content. Glandular trichomes, which are specialized structures on leaves and flowers, undergo morphological changes during flower maturation. Stalked trichomes, which develop from sessile precursors, are associated with higher cannabinoid and monoterpene production, and their density increases notably during flowering Hesami2023Livingston2019.
Variation and Taxonomy: Leaf Morphology and Chemical Traits
Cannabis displays extensive variation in leaf morphology, branching patterns, and chemical composition. However, studies show that in hybrid populations, commonly assumed correlations between leaf morphology and chemical properties (such as cannabinoid content) do not hold. This suggests that naming conventions and legal classifications based on leaf shape are unreliable for predicting chemical properties, especially in modern hybrids Holloway2021Vergara2021.
Conclusion
Cannabis leaf morphology is a complex trait influenced by developmental stage, genetic regulation, and environmental factors like photoperiod. While leaf shape and structure change predictably through the plant’s life cycle, these traits do not reliably indicate chemical composition in hybrid plants. Understanding the genetic and developmental basis of leaf morphology is essential for both research and industrial applications, but new classification systems are needed to accurately reflect the diversity and properties of modern cannabis varieties Hesami2023Hesami2024Holloway2021+1 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.
Peer Review #1 of "Widely assumed phenotypic associations in Cannabis sativa lack a shared genetic basis (v0.1)"
Many traits in Cannabis sativa, such as leaf morphology, are not strongly correlated in hybrid populations, suggesting a need for a new system for identifying variation and legal regulation.
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