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Despite their key phylogenetic position and their unique biology, hornworts have been widely overlooked. Until recently there was no hornwort model species amenable to systematic experimental investigation.Anthoceros agrestishas been proposed as the model species to study hornwort biology.

Extant land plants consist of two deeply divergent groups, tracheophytes and bryophytes, which shared a common ancestor some 500 million years ago. While information about vascular plants and the two of the three lineages of bryophytes, the mosses and liverworts, is steadily accumulating, the biology of hornworts remains poorly explored. Yet, as the sister group to liverworts and mosses, hornworts are critical in understanding the evolution of key land plant traits. Until recently, there was no hornwort model species amenable to systematic experimental investigation, which hampered detailed insight into the molecular biology and genetics of this unique group of land plants. The emerging hornwort model species,Anthoceros agrestis, is instrumental in our efforts to better understand not only hornwort biology but also fundamental questions of land plant evolution. To this end, here we provide an overview of hornwort biology and current research on the model plantA. agrestisto highlight its potential in answering key questions of land plant biology and evolution.

Hornworts are crucial to understand the phylogeny of early land plants. The emergence of ‘reverse’ U‐to‐C RNA editing accompanying the widespread C‐to‐U RNA editing in plant chloroplasts and mitochondria may be a molecular synapomorphy of a hornwort–tracheophyte clade. C‐to‐U RNA editing is well understood after identification of many editing factors in models likeArabidopsis thalianaandPhyscomitrella patens, but there is no plant model yet to investigate U‐to‐C RNA editing. The hornwortAnthoceros agrestisis now emerging as such a model system.

Marchantia polymorphahas recently become a prime model for cellular, evo‐devo, synthetic biological, and evolutionary investigations. We present a pseudomolecule‐scale assembly of theM. polymorphagenome, making comparative genome structure analysis and classical genetic mapping approaches feasible. We anchored 88% of theM. polymorphadraft genome to a high‐density linkage map resulting in eight pseudomolecules. We found that the overall genome structure ofM. polymorphais in some respects different from that of the model mossPhyscomitrella patens. Specifically, genome collinearity between the two bryophyte genomes and vascular plants is limited, suggesting extensive rearrangements since divergence. Furthermore, recombination rates are greatest in the middle of the chromosome arms inM. polymorphalike in most vascular plant genomes, which is in contrast withP. patenswhere recombination rates are evenly distributed along the chromosomes. Nevertheless, some other properties of the genome are shared withP. patens. As inP. patens, DNA methylation inM. polymorphais spread evenly along the chromosomes, which is in stark contrast with the angiosperm modelArabidopsis thaliana, where DNA methylation is strongly enriched at the centromeres. Nevertheless, DNA methylation and recombination rate are anticorrelated in all three species. Finally,M. polymorphaandP. patenscentromeres are of similar structure and marked by high abundance of retroelements unlike in vascular plants. Taken together, the highly contiguous genome assembly we present opens unexplored avenues forM. polymorpharesearch by linking the physical and genetic maps, making novel genomic and genetic analyses, including map‐based cloning, feasible.