The directional growth response of plants toward or away from light sources. This allows plants to optimize their light exposure for photosynthesis by bending stems and leaves toward bright light.
Coined in the 1880s from Greek 'photos' (light) and 'tropos' (turn, direction). The term was created as botanists began understanding that plant movements weren't random but were specific responses to environmental stimuli.
Plants can actually 'see' light direction better than you might think - they can detect light differences as small as 1% between different sides of their stems! The famous sunflower tracking the sun is just the most obvious example of phototropism in action.
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