The study found that urban trees are a critical element in reducing air pollution. Four common houseplants were used in both the laboratory and residential experiments: ficus (Ficus benjamina); golden pothos (Epipremnum aureum); spider fern (Chlorophytus comsosum ‘vittatum’); and Christmas cactus (Schlumbergera truncate‘harmony’).The plants were selected because they are commonly available, are hardy, have relatively low light requirements and vary in leaf morphology.