Human-mediated vegetative dispersal of the liverwort Riccia treubiana in a tropical city

Bryophyte dispersal in urban environments is poorly understood, particularly in the tropics. A thalloid liverwort, Riccia treubiana , exhibits a patchy yet recurring presence in Singapore, a tropical city state situated just 1.03 degrees north of the Equator. This study investigated the liverwort distribution and fragment-based dispersal in Singapore, providing the first experimental evidence of dispersal mechanisms in Riccia . Field surveys recorded 35 new occurrences, of which 90% were found in soil-filled gaps between parking lot pavers. Regeneration trials confirmed that both apical and middle segments have the potential to fully regenerate. Simulated footstep and vehicle-crushing experiments demonstrated that vegetative fragments can be transferred and successfully established via human and vehicular movements. Shoe sole design significantly influenced fragment retention and deposition efficiency, while vehicle tyres deposited most fragments within the first meter post-contact. Notably, fragments appeared more often near paver edges, suggesting high-friction interfaces aid initial deposition. Its absence at some previously known sites may be due to habitat loss from recent surface renovation, reduced disturbance, dense vascular plant competition, or prolonged sun exposure. These findings emphasise how dispersal, microhabitat, and urban renewal interact to shape bryophytes’ presence, offering insights for conserving them in tropical cities.