The origins of early land plant lifeforms and their classical and molecular phylogenies, still provide a number of intriguing questions and opportunities for investigations using modern day bryophyte representatives. Using real-time measurements of CO2/H2O exchange and stable isotope composition, we have developed systems to quantify the interplay between liquid phase and mesophyll limitations across thalloid material. These models couple photosynthetic activation, water loss, assimilation and productivity. Their use in variety of habitats will be demonstrated, in determining palaeohistorical performance in Antarctic mosses and altitudinal gradients of tropical epiphytic bryophytes in Peru. We have previously demonstrated their application for contrasting thalloid lifeforms, including changes between thalloid and ventilated liverworts, and a comparison between hornworts and the occurrence of a biophysical carbon concentrating mechanism(CCM). In a re-evaluation of hornwort phylogeny, we explore the relationship between the development of multiplastidicity and CCM occurrence. Ultimately, whether the CCM is a relict of an algal ancestor, and the apparent loss or gain of a CCM around 320 mya, provide intriguing questions for the development of stomata, xylem and ventilation of intracellular air spaces, traits which lead to sporophyte dominance in other land plant lineages.