An integrative taxonomic study of the genus Lethocolea (Marchantiophyta: Acrobolbaceae)

Background and aims – Lethocolea (Acrobolbaceae) is a small liverwort genus of seven species distributed in temperate regions of the Southern Hemisphere and on tropical mountains. The taxonomic history of the genus has been chaotic, the species were described under many different names and have been distinguished mainly based on geography. Here, we undertook a taxonomic revision of the genus based on a reassessment of morphological characters and a molecular analysis. Material and methods – Type material and additional collections from 17 herbaria were examined in the morphological study. Sequences of the rps4 chloroplast region and maximum likelihood analyses were used to reconstruct the phylogeny. Key results and conclusions – Two fully supported clades were resolved within Lethocolea lending support to the recognition of two subgenera, subgen. Lethocolea and subgen. Symphyomitra. Lethocolea congesta from Africa, and L. glossophylla and L. radicosa from America exhibited considerable morphological overlap and were not distinguishable based on rps4 sequences. The latter two species are reduced into synonymy with L. congesta, whose range spans across Africa, the Neotropics and southern South America. In Australasia, where only one species, L. pansa, is recognized, two morphotypes were found. The first one, with a smooth cuticle, wingless gemmae, and leaf cells without trigones, is identical to the type of L. pansa and occurs in Australia and New Zealand. In addition, the species is newly reported from South Africa. The second morphotype has a papillose cuticle, winged gemmae, and leaf cells with distinct trigones, and is assigned to L. javanica, which ranges across Australasia and furthermore occurs in Java and India. The recognition of these two species is supported by molecular analysis. Altogether, we recognize four species within Lethocolea, which are thoroughly described, illustrated, and keyed. We present 12 new lectotypifications.