New insights into the phylogeny of the complex thalloid liverworts (Marchantiopsida) based on chloroplast genomes.

Marchantiopsida (complex thalloid liverworts) are one of the earliest lineages of embryophytes (land plants), and well-known for their air pores and chambers, pegged rhizoids, and absence of organellular RNA editing sites. Despite their importance to an understanding of early embryophyte evolution, many key nodes within this class remain poorly resolved, owing to the paucity of genetic loci previously available for phylogenetic analyses. Here, we sequenced 54 plastomes, representing 28 genera, nearly all families, and all orders of Marchantiopsida. Based on these plastomes, we present a hypothesis of deep relationships within the class, and make the first investigations of gene contents and synteny. Overall, the Marchantiopsida plastomes were well-conserved, with the exception of the genus Cyathodium that has plastomes with higher GC content, fewer single sequence repeats (SSRs), and more structural variations, implying that this genus might possess RNA editing sites. Abundant repetitive elements and six highly divergent regions were identified as suitable for future infrafamilial taxonomic studies. The phylogenetic topology of Sphaerocarpales, Neohodgsoniales and Blasiales within Marchantiopsida was essentially congruent with previous studies but generally we obtained higher support values. Based on molecular evidence and previous morphological studies, we include Lunulariales in Marchantiales and suggest the retention of narrowed delimitation of monotypic families. The phylogenetic relationships within Marchantiales were better resolved, and 13 monophyletic families were recovered. Our analyses confirmed that the loss of intron 2 of ycf3 is a synapomorphy of Marchantiidae. Finally, we propose a new genus, Asterellopsis (Aytoniaceae), and present an updated classification of Marchantiopsida. The highly supported phylogenetic backbone provided here establishes a framework for future comparative and evolutionary studies of the complex thalloid liverworts.

Molecular Phylogenetics and the Evolution of Morphological Complexity in Aytoniaceae (Marchantiophyta).

Aytoniaceae are one of the largest families of complex thalloid liverworts (Marchantiopsida), consisting of about 70 species, with most species being distributed in temperate areas. However, the phylogeny and evolution of the morphological character of Aytoniaceae are still poorly understood. Here, we employed two chloroplast loci, specifically, rbcL and trnL-F, along with a 26S nuclear ribosomal sequence to reconstruct the phylogeny and track the morphological evolution of Aytoniaceae. Our results reveal that Aytoniaceae are monophyletic, and five monophyletic clades were recovered (i.e., Asterellopsis-Cryptomitrium, Calasterella, Mannia, Reboulia-Plagiochasma, and Asterella). Asterella was divided into five clades (i.e., Asterella lindenbergiana, subg. Saccatae, subg. Phragmoblepharis, subg. Wallichianae, and subg. Asterella), except for Asterella palmeri, which is the sister of Asterellopsis grollei. Bayesian molecular clock dating indicates that the five primary clades within Aytoniaceae underwent divergence events in the Cretaceous period. Asterellopsis differentiated during the early Upper Cretaceous (c. 84.2 Ma), and Calasterella originated from the late Lower Cretaceous (c. 143.0 Ma). The ancestral Aytoniaceae plant is reconstructed as the absence of a pseudoperianth, lacking equatorial apertures, and having both male and female reproductive organs on the main thallus. At present, Asterellopsis consists of two species known in Asia and America with the new transfer of Asterella palmeri to Asterellopsis. A new subgenus, Asterella subg. Lindenbergianae, is proposed.