The surprising appearance of <em>Riccia cavernosa</em> (Ricciaceae) in North American pavement cracks

Urbanization alters and homogenizes species distributions but can unexpectedly create new niches for plant species as well. In 2016, Riccia cavernosa, a liverwort known in Vermont only from historical records made in natural habitats over a century ago, was unexpectedly discovered growing in the cracks of cement walkways in the city of Burlington. To investigate the identity and origin of these urban populations, a phylogenetic study was conducted using DNA barcoding of two chloroplast regions (rbcL and trnL-trnF), including specimens from Britain, Latvia, Australia, as well as other new collections from riparian habitat in Vermont located during our investigation. Our phylogenetic analysis corroborates the identification of the specimens from both the urban and natural habitats as R. cavernosa, marking its first records in Vermont in over 100 years. Our field observations indicate that R. cavernosa is now well-established in anthropic urban habitats in Vermont, which is a dramatic turn of events for this previously rare plant. The origins of these urban populations are unclear, but the findings raise intriguing questions about the potential adaptation of this species to anthropic landscapes. Further research with population-level sampling is needed to address these questions.