Phylogeny and diversification of bryophytes

Abstract

The bryophytes comprise three phyla of embryophytes that are well established to occupy the first nodes among extant lineages in the land-plant tree of life. The three bryophyte groups (hornworts, liverworts, mosses) may not form a monophyletic clade, but they share life history features including dominant free-living gametophytes and matrotrophic monosporangiate sporophytes. Because of their unique vegetative and reproductive innovations and their critical position in embryophyte phylogeny, studies of bryophytes are crucial to understanding the evolution of land plant morphology and genomes. This review focuses on phylogenetic relationships within each of the three divisions of bryophytes and relates morphological diversity to new insights about those relationships. Most previous work has been on the mosses, but progress on understanding the phylogeny of hornworts and liverworts is advancing at a rapid pace. Multilocus multigenome studies have been successful at resolving deep relationships within the mosses and liverworts, whereas single-gene analyses have advanced understanding of hornwort evolution.

Newly resolved relationships in an early land plant lineage: Bryophyta class Sphagnopsida (peat mosses)

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Phylogenetic analyses of genome structure and nucleotide sequences from mitochondrial, plastid, and nuclear genes have corroborated the view held by botanists for over a century that the bryophyte groups (mosses, liverworts, hornworts) comprise early-diverging land plant lineages that originated before the appearance of vascular plants ( Haeckel, 1876 ;Campbell, 1895 ;Bower, 1935 ;Kenrick and Crane, 1997 ;Shaw and Renzaglia, 2004 ). Early cladistic analyses based on morphological characters ( Mishler and Churchill, 1984 ) showed that the three bryophyte groups, classifi ed by most botanists of the time as a single phylum because of their similar gametophyte-dominant life cycles, more likely represent a paraphyletic grade that diverged before the emergence of the vascular plants.

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“…In fact, Haeckel ' s (1876) tree similarly shows mosses and liverworts as a paraphyletic grade basal to the vascular plants. Recent data sets appear to favor the hypothesis that liverworts (phylum Marchantiophyta) comprise the earliest-diverging lineage, followed by the mosses (Bryophyta) and hornworts (Anthocerophyta) ( Qiu et al, 1998 ;Nickrent et al, 2000 ;Shaw and Renzaglia, 2004 ). However, the most data-rich studies to date, based on chloroplast or mitochondrial organellar proteins, like analyses based on sperm cell morphology ( Garbary et al, 1993 ), identify a clade uniting liverworts and mosses, and additional data are still needed before we can consider the branching order of early land plant lineages to be fi nally resolved ( Nishiyama et al, 2004 ;Rodr í guez-Ezpeleta et al, 2007 ;Terasawa et al, 2007 ; but see also Qiu, et al, 2006 ).…”

Invasion of the continents: cyanobacterial crusts to tree-inhabiting arthropods

“…Molecularly based phylogenetic analyses and studies of the cell-wall microstructure of embryophjrtes and related algal clades indicate that charophytes, a green algal clade, are the closest extant relatives of embryophytes [40,42,43] (Box 1). Depending on the study, any of three major bryophyte lineages (liverworts, hornworts or mosses) might be the sister group to vascular plants [40,[44][45][46][47], consistent with the view that bryophytes are a grade rather than a clade [47]. After bryophyte establishment, one to a few extinct groups of protracheophytes diverged [7], one of which gave rise to a monophyletic vascularplant clade defined by robust synapomorphies [45].…”

A brief history of the cryptogams of Fiji and prospects for the future

“…Marchantiophyta (liverworts), Anthocerotophyta (hornworts), and Bryophyta (mosses) (e.g. Mishler & Churchill 1984, Kenrick & Crane 1997, Shaw & Renzaglia 2004, Qiu et al 2007. Similarly, those plants historically classified as 'pteridophytes' and 'ferns and fern allies'represent a paraphyletic assemblage, including the lycophytes, horsetails, whisk ferns, and all eusporangiate and leptosporangiate ferns (Smith et al 2006).…”