This study compares the photosynthetic performance and frond development of Lemna gibba (LG6), Lemna minor (LM16), and Spirodela polyrhiza (SP3) under two temperature treatments, 20 °C and 35 °C. Using chlorophyll-fluorescence imaging and ImageJ-based digital analysis, the research quantifies changes in PSII efficiency (Fv/Fm, Y(II)) and frond-level spatial patterns. Results show that all three clones experienced reduced frond size and lower photosynthetic efficiency at 35 °C, confirming strong heat-induced stress. Among the species, SP3 displayed the highest tolerance, LM16 showed intermediate sensitivity, and LG6 was most inhibited under elevated temperature. Spatial fluorescence maps further revealed localized photoinhibition at 35 °C, which was not visible from whole-frond averages alone