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• Premise of the study: Separating sexual function between different individuals carries risks, especially for sedentary organisms. Nevertheless, many land plants have unisexual gametophytes or sporophytes. This study brings together data and theoretical insights from research over the past 20 yr on the occurrence and frequency of plant sexual systems, focusing on the flowering plants.• Methods: A list of genera with dioecious species, along with other information, is made available (http://www.umsl.edu/∼renners/). Frequencies of other sexual systems are tabulated, and data on the genetic regulation, ecological context, and theoretical benefits of dioecy reviewed.• Key results: There are 15600 dioecious angiosperms in 987 genera and 175 families, or 5–6% of the total species (7% of genera, 43% of families), with somewhere between 871 to 5000 independent origins of dioecy. Some 43% of all dioecious angiosperms are in just 34 entirely dioecious clades, arguing against a consistent negative influence of dioecy on diversification. About 31.6% of the dioecious species are wind-pollinated, compared with 5.5–6.4% of nondioecious angiosperms. Also, 1.4% of all angiosperm genera contain dioecious and monoecious species, while 0.4% contain dioecious and gynodioecious species. All remaining angiosperm sexual systems are rare. Chromosomal sex determination is known from 40 species; environmentally modulated sex allocation is common. Few phylogenetic studies have focused on the evolution of dioecy.• Conclusions: The current focus is on the genetic mechanisms underlying unisexual flowers and individuals. Mixed strategies of sexual and vegetative dispersal, together with plants’ sedentary life style, may often favor polygamous systems in which sexually inconstant individuals can persist. Nevertheless, there are huge entirely dioecious clades of tropical woody plants.

The feasibility, benefits, risks, and consequences of using sporeless sporophytes to aid the upscaling of kelp cultivation in Europe and North America, as well as the barriers that currently exist and how these may be overcome, are reviewed here. Taking environmental, industrial, and regulatory factors into account, we will discuss the use of domesticated sporeless sporophytes as an asset to facilitate upscaling kelp cultivation without potentially impacting wild genetic diversity.

Bull kelp (Nereocystis luetkeana) possesses a heteromorphic lifecycle that alternates between two phases: a large, diploid sporophyte and a microscopic, haploid gametophyte. Recent research has suggested that bull kelp may be capable of bypassing the microscopic gametophytic stage via the direct release of structures identified in the literature as embryonic sporophytes. In order to verify the identity of these structures, we isolated and cultured multiple directly released structures over the course of three weeks in the lab and monitored their growth and development. We were able to track 67 directly released structures for more than one time interval, and found no evidence that the development of these structures followed that of embryonic sporophytes. We present the alternative hypothesis that these directly released structures are sporangia that have not yet released their spores. We conclude that even with the direct release of microscopic structures such as sporangia, there is currently no evidence that bull kelp are bypassing their established biphasic life history.

The colonization of land by plants shaped the terrestrial biosphere, the geosphere and global climates. The nature of morphological and molecular innovation driving land plant evolution has been an enigma for over 200 years. Recent phylogenetic and palaeobotanical advances jointly demonstrate that land plants evolved from freshwater algae and pinpoint key morphological innovations in plant evolution. In the haploid gametophyte phase of the plant life cycle, these include the innovation of mulitcellular forms with apical growth and multiple growth axes. In the diploid phase of the life cycle, multicellular axial sporophytes were an early innovation priming subsequent diversification of indeterminate branched forms with leaves and roots. Reverse and forward genetic approaches in newly emerging model systems are starting to identify the genetic basis of such innovations. The data place plant evo-devo research at the cusp of discovering the developmental and genetic changes driving the radiation of land plant body plans. This article is part of the themed issue ‘Evo-devo in the genomics era, and the origins of morphological diversity’.

Platycerium wallichii Hook is a rare and endangered tropical epiphytic fern with ornamental and medicinal value. It is usually propagated by spore germination to produce sporophytes. This study established an in vitro protocols for spore germination, leading to filament formation and development of prothallia, and finally development of sporophytes following fertilization. The prothallia could be proliferated by 8.7 time within 30 days. The development of archegonia and antheridia on prothallia was asynchronous and prothallia were mainly dioecious (over 90%) and to a lesser extent hermaphroditic (5%). Prothallia were subcultured and propagated on plant growth regulator (PGR)-free Murashige and Skoog (MS) medium before fertilization. After fertilization, the frond lobes of in vitro sporophytes, which were used as explants, induced green globular bodies (GGBs) and adventitious sporophyte buds (ASBs). Among the PGRs tested, 1.0 mg L− 1 6-benzyladenine (BA) induced the most ASBs (16.7 per frond) and 1.0 mg L− 1 thidiazuron (TDZ) induced the largest number of GGBs (17.7 per frond), while 2,4-dichlorophenoxyacetic acid (2,4-D) induced the fewest ASBs and GGBs (12.8 per frond) and α-naphthaleneacetic acid (NAA) induced only a few ASBs (12.6 per frond), with mostly formation of rhizoids. When root sections were used as explants, optimal ASB induction required MS medium with 0.3 mg L− 1 BA and 0.1 mg L− 1 NAA and SPC could reach 5.7 within 60 d. Sporophytes could also be proliferated from rhizomes on the optimal MS medium with 0.3 mg L− 1 BA and its sporophyte proliferation coefficient (SPC) could reach 6.3 within 45 d. When ½MS medium was supplemented with 0.3–1.0 mg L− 1 NAA or indole-3-butyric acid (IBA), rooting of sporophytes was essentially 100%. After wrapping rhizomes in moss and transplanting them to a humus and river sand (1: 1, v/v) substrate, 100% of the plantlets survived after one month (98.7% after three months). The regeneration protocols presented in this work have a potential to assist in for the conservation and propagation of this endangered horticultural and medicinal fern.

• Unraveling the phylogenetic relationships between the four major lineages of terrestrial plants (mosses, liverworts, hornworts, and vascular plants) is essential for an understanding of the evolution of traits specific to land plants, such as their complex life cycles, and the evolutionary development of stomata and vascular tissue. • Well supported phylogenetic hypotheses resulting from different data and methods are often incongruent due to processes of nucleotide evolution that are difficult to model, for example substitutional saturation and composition heterogeneity. We reanalysed a large published dataset of nuclear data and modelled these processes using degenerate-codon recoding and tree-heterogeneous composition substitution models. • Our analyses resolved bryophytes as a monophyletic group and showed that the nonnonmonophyly of the clade that is supported by the analysis of nuclear nucleotide data is due solely to fast-evolving synonymous substitutions. • The current congruence among phylogenies of both nuclear and chloroplast analyses lent considerable support to the conclusion that the bryophytes are a monophyletic group. An initial split between bryophytes and vascular plants implies that the bryophyte life cycle (with a dominant gametophyte nurturing an unbranched sporophyte) may not be ancestral to all land plants and that stomata are likely to be a symplesiomorphy among embryophytes.

BACKGROUND: Land plants (embryophytes) evolved from streptophyte green algae, a small group of freshwater algae ranging from scaly, unicellular flagellates (Mesostigma) to complex, filamentous thalli with branching, cell differentiation and apical growth (Charales). Streptophyte algae and embryophytes form the division Streptophyta, whereas the remaining green algae are classified as Chlorophyta. The Charales (stoneworts) are often considered to be sister to land plants, suggesting progressive evolution towards cellular complexity within streptophyte green algae. Many cellular (e.g. phragmoplast, plasmodesmata, hexameric cellulose synthase, structure of flagellated cells, oogamous sexual reproduction with zygote retention) and physiological characters (e.g. type of photorespiration, phytochrome system) originated within streptophyte algae. RECENT PROGRESS: Phylogenetic studies have demonstrated that Mesostigma (flagellate) and Chlorokybus (sarcinoid) form the earliest divergence within streptophytes, as sister to all other Streptophyta including embryophytes. The question whether Charales, Coleochaetales or Zygnematales are the sister to embryophytes is still (or, again) hotly debated. Projects to study genome evolution within streptophytes including protein families and polyadenylation signals have been initiated. In agreement with morphological and physiological features, many molecular traits believed to be specific for embryophytes have been shown to predate the Chlorophyta/Streptophyta split, or to have originated within streptophyte algae. Molecular phylogenies and the fossil record allow a detailed reconstruction of the early evolutionary events that led to the origin of true land plants, and shaped the current diversity and ecology of streptophyte green algae and their embryophyte descendants. CONCLUSIONS: The Streptophyta/Chlorophyta divergence correlates with a remarkably conservative preference for freshwater/marine habitats, and the early freshwater adaptation of streptophyte algae was a major advantage for the earliest land plants, even before the origin of the embryo and the sporophyte generation. The complete genomes of a few key streptophyte algae taxa will be required for a better understanding of the colonization of terrestrial habitats by streptophytes.

Kelp forests are being degraded and/or lost in many regions, and as such, interest in active kelp restoration approaches to reinstate forests is growing. ‘Green gravel’ is a promising new kelp restoration technique that involves seeding small rocks with kelp zoospores, rearing the gametophyte and juvenile sporophyte stages in aquaria before outplanting them at restoration sites. However, to be considered a viable approach to kelp forest restoration, the efficacy of this technique needs to be assessed across a range of environmental contexts and kelp species. Here, we aimed to understand the utility of green gravel as a kelp restoration technique for wave-exposed intertidal shores. Two substrate types – gravel and cobbles – were seeded with Saccharina latissima, reared in the aquarium and outplanted at two sites along the northeast coast of England. Outplanted rocks were monitored for retention, and the density and length of S. latissima. Juvenile sporophytes persisted on both rock types, although declines in density and variations in length were observed over time. Substrate retention was low, with gravel more likely to be removed from restoration sites compared to cobbles, and all outplanted rocks were lost after eight months. While our initial testing of the green gravel restoration technique on wave-exposed shores was not successful, our results provide important insights for developing/refining the technique and a baseline for comparison for future efforts. However, prior to commencing large-scale kelp restoration in wave-exposed areas using green gravel, further testing of the technique and comparisons with other restoration approaches are needed.

The basal land plant Marchantia polymorpha efficiently propagates in favourable environments through clonal progeny called gemmae. Gemmae develop in cup-shaped receptacles known as gemma cups, which are formed on the gametophyte body. Anatomical studies have described the developmental processes involved over a century ago; however, little is known about the underlying molecular mechanisms. Recent studies have started to unravel the mechanism underlying genetic and hormonal regulation of gemma cup and gemma development, showing that it shares some regulatory mechanisms with several sporophytic organs in angiosperms. Further study of these specialized organs will contribute to our understanding of the core regulatory modules underlying organ development in land plants and how these became so diversified morphologically over the course of evolution.

Kelp systems dominate nearshore marine environments in upwelling zones characterized by cold temperatures and high nutrients. Worldwide, kelp population persistence and recruitment success generally decreases with rising water temperatures coupled with low nutrients, making kelp populations vulnerable to impending warming of the oceans. This response to climate change at a global scale, however, may vary due to regional differences in temperature variability, acclimation, and differential responses of kelp species to changing conditions. Culture experiments were conducted on 12 eastern Pacific kelp taxa across geographic regions (British Columbia, central California, and southern California) under three nitrate levels (1, 5, and 10 μmol/L) and two temperatures (12°C and 18°C) to determine sporophyte production (i.e., recruitment success). For all taxa from all locations, sporophytes were always present in the 12°C treatment and when recruitment failure was observed, it always occurred at 18°C, regardless of nitrate level, indicating that temperature is the driving factor limiting recruitment, not nitrate. Rising ocean temperatures will undoubtedly cause recruitment failure for many kelp species; however, the ability of species to acclimatize or adapt to increased temperatures at the warmer edge of their species range may promote a resiliency of kelp systems to climate change at a global scale.