An unusual new rheophytic species of the liverwort genus <em>Cephaloziella</em> from Panama

During bryophyte surveys in the Antón River watershed, Coclé Province, Panama, we discovered a minute rheophytic liverwort representing an undescribed species of Cephaloziellaceae. Phylogenetic analyses based on nuclear ITS1–2 and plastid rbcL DNA markers placed the new species within Cephaloziella, where it resolved in a clade with C. microphylla, C. kiaeri, and C. recurvifolia in the ITS tree, and with C. microphylla alone in the rbcL tree. We describe the species as Cephaloziella minutiloba A.M. Sierra, Gradst. & Gudiño sp. nov. The new species is morphologically distinct by its minute size, flagelliform shoots, scattered violet rhizoids, succubous and highly unequally conduplicate leaves with a prominent ventral lobe and a strongly reduced dorsal lobe bent over the ventral lobe, and crenate-dentate leaf margins. The gynoecia on short ventral branches are made up of 2–3 series of highly connate, crenate bracts and a 5-plicate perianth with a fringed mouth. This new species expands our understanding of morphological diversity and rheophytic adaptation within Cephaloziella. The morphological affinities of the species are discussed, and the importance of integrative taxonomic approaches in liverwort systematics is emphasized.