Indoor air quality has become a growing concern as people are spending more time 18 indoors, combined with the construction of highly sealed buildings that promote 19 thermal efficiency. Particulate matter (PM) is a common indoor air pollutant, with 20 exposure to high concentrations associated with several detrimental health outcomes. 21 Active botanical biofilters or functional green walls are becoming increasingly 22 efficient and have the potential to mitigate high suspended PM concentrations. These 23 systems, however, require further development before they become competitive with 24 industry standard in-room air filters. Whilst the plant growth substrate in active 25 biofilters can act as a filter medium, it was previously not known whether the plant 26 component of these systems played a function in PM filtration. This study thus 27 examines the influence of the botanical component on active green wall PM single 28 pass removal efficiency (SPRE), with a focus on evaluating the air filtration features 29 of different plant species in green wall modules. All tested botanical biofilters 30 outperformed biofilters that consisted only of substrate. Green walls using different 31 plant species had different single pass removal efficiencies, with fern species 32 recording the highest removal efficiencies across all measured particle sizes 33 (Nephrolepis exaltata bostoniensis SPRE for PM0.3-0.5 and PM5-10 = 45.78% and 34 92.46% respectively). Higher removal efficiencies were associated with increased 35 pressure drop across the biofilter. An assessment of plant morphological data 36 suggested that the root structure of the plants strongly influenced removal efficiency. 37 These findings demonstrate the potential to enhance active botanical biofiltration 38 technology with appropriate plant species selection.