In botany, describing the upper surface of a leaf or other plant part that is oriented toward the main stem or axis.
From Latin prefix 'ad-' (toward) plus 'axial' (relating to an axis); coined in botanical terminology during the 18th century as plants were being scientifically classified.
Plants have a 'top' and 'bottom' at the microscopic level—adaxial leaves face inward toward the plant's center, and knowing this distinction lets botanists predict exactly how photosynthesis is organized.
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