Symptoms of edema in houseplants
Plants may develop wart-like or crusty raised bumps or blisters on the lower leaf surfaces. The bumps may become brown or necrotic and may be misdiagnosed as disease or insect feeding damage. This is a physiological disorder that occurs when water absorbed by a plant's roots exceeds the amount of water lost through the leaves.
Management
Allow adequate drying time between watering schedules especially when growing media temperatures are cool and air temperatures are warm. Bottom heat can help alleviate edema symptoms during the winter. Plants prone to edema include English ivy, Geranium, Schefflera, jade, snake plant, African violets, Pellionia, and aluminum plant.