The challenging but unique eco-evolutionary aspects of Sphagnum moss

Sphagnum is emerging as a useful system for advancing knowledge at the interface between ecology and evolutionary biology. Here, we explore: the importance of the Sphagnum microbiome to ecosystem structure and function; the value of naturally occurring genetic variation within Sphagnum populations; and the ongoing process of speciation and ecological divergence in the genus. Recent advances in understanding the molecular genetics underpinning cyanobacteria associations with Sphagnum's living and hyaline cells make this a rich area for future research, including implications for carbon and nitrogen exchange. We review niche differentiation in Sphagnum, underlying functional traits, and phylogenetic conservation. More knowledge is needed about naturally occurring variation within Sphagnum species, including trait plasticity and variation between sexes, to explore broader issues such as the mechanisms underpinning metabolism and its consequences for microbiomes as well as how we can most effectively use Sphagnum in restoration and other ecological problem solving. We use newly resolved phylogenetic relationships within the S. magellanicum complex to illustrate its potential for studying ecologically driven speciation. Our review focuses on the unique challenges in using Sphagnum as an eco-evolutionary system but also offers insights into emerging questions across genetics, physiological traits, ecological function, and biogeochemical cycling.