Phylogenetic niche conservatism in C4 grasses

Photosynthetic pathway is used widely to discriminate plant functional types in studies of global change. However, independent evolutionary lineages of C₄ grasses with different variants of C₄ photosynthesis show different biogeographical relationships with mean annual precipitation, suggesting phylogenetic niche conservatism (PNC). To investigate how phylogeny and photosynthetic type differentiate C₄ grasses, we compiled a dataset of morphological and habitat information of 185 genera belonging to two monophyletic subfamilies, Chloridoideae and Panicoideae, which together account for 90 % of the world’s C₄ grass species. We evaluated evolutionary variance and covariance of morphological and habitat traits. Strong phylogenetic signals were found in both morphological and habitat traits, arising mainly from the divergence of the two subfamilies. Genera in Chloridoideae had significantly smaller culm heights, leaf widths, 1,000-seed weights and stomata; they also appeared more in dry, open or saline habitats than those of Panicoideae. Controlling for phylogenetic structure showed significant covariation among morphological traits, supporting the hypothesis of phylogenetically independent scaling effects. However, associations between morphological and habitat traits showed limited phylogenetic covariance. Subfamily was a better explanation than photosynthetic type for the variance in most morphological traits. Morphology, habitat water availability, shading, and productivity are therefore all involved in the PNC of C₄ grass lineages. This study emphasized the importance of phylogenetic history in the ecology and biogeography of C₄ grasses, suggesting that divergent lineages need to be considered to fully understand the impacts of global change on plant distributions.     

Evolutionary innovations driving abiotic stress tolerance in C4 grasses and cereals

Grasslands dominate the terrestrial landscape, and grasses have evolved complex and elegant strategies to overcome abiotic stresses. The C₄ grasses are particularly stress tolerant and thrive in tropical and dry temperate ecosystems. Growing evidence suggests that the presence of C₄ photosynthesis alone is insufficient to account for drought resilience in grasses, pointing to other adaptations as contributing to tolerance traits. The majority of grasses from the Chloridoideae subfamily are tolerant to drought, salt, and desiccation, making this subfamily a hub of resilience. Here, we discuss the evolutionary innovations that make C₄ grasses so resilient, with a particular emphasis on grasses from the Chloridoideae (chloridoid) and Panicoideae (panicoid) subfamilies. We propose that a baseline level of resilience in chloridoid ancestors allowed them to colonize harsh habitats, and these environments drove selective pressure that enabled the repeated evolution of abiotic stress tolerance traits. Furthermore, we suggest that a lack of evolutionary access to stressful environments is partially responsible for the relatively poor stress resilience of major C₄ crops compared to their wild relatives. We propose that chloridoid crops and the subfamily more broadly represent an untapped reservoir for improving resilience to drought and other abiotic stresses in cereals.

Chloridoid grasses have evolved unique adaptations to adverse environments and represent an untapped reservoir for improving resilience to drought and other abiotic stresses in cereals.     

Photosynthetic innovation broadens the niche within a single species

Adaptation to changing environments often requires novel traits, but how such traits directly affect the ecological niche remains poorly understood. Multiple plant lineages have evolved C₄ photosynthesis, a combination of anatomical and biochemical novelties predicted to increase productivity in warm and arid conditions. Here, we infer the dispersal history across geographical and environmental space in the only known species with both C₄ and non‐C₄ genotypes, the grass Alloteropsis semialata. While non‐C₄ individuals remained confined to a limited geographic area and restricted ecological conditions, C₄ individuals dispersed across three continents and into an expanded range of environments, encompassing the ancestral one. This first intraspecific investigation of C₄ evolutionary ecology shows that, in otherwise similar plants, C₄ photosynthesis does not shift the ecological niche, but broadens it, allowing dispersal into diverse conditions and over long distances. Over macroevolutionary timescales, this immediate effect can be blurred by subsequent specialisation towards more extreme niches.     

Evolution of the C4 photosynthetic pathway: events at the cellular and molecular levels

The biochemistry and leaf anatomy of plants using C₄ photosynthesis promote the concentration of atmospheric CO₂ in leaf tissue that leads to improvements in growth and yield of C₄ plants over C₃ species in hot, dry, high light, and/or saline environments. C₄ plants like maize and sugarcane are significant food, fodder, and bioenergy crops. The C₄ photosynthetic pathway is an excellent example of convergent evolution, having evolved in multiple independent lineages of land plants from ancestors employing C₃ photosynthesis. In addition to C₃ and C₄ species, some plant lineages contain closely related C₃–C₄ intermediate species that demonstrate leaf anatomical, biochemical, and physiological characteristics between those of C₃ plants and species using C₄ photosynthesis. These groups of plants have been extremely useful in dissecting the modifications to leaf anatomy and molecular biology, which led to the evolution of C₄ photosynthesis. It is now clear that great variation exists in C₄ leaf anatomy, and diverse molecular mechanisms underlie C₄ biochemistry and physiology. However, all these different paths have led to the same destination—the expression of a C₄ CO₂ concentrating mechanism. Further identification of C₄ leaf anatomical traits and molecular biological components, and understanding how they are controlled and assembled will not only allow for additional insights into evolutionary convergence, but also contribute to sustainable food and bioenergy production strategies.     

Influence of salt stress on C4 photosynthesis in Miscanthus sinensis Anderss.

• Miscanthus sinensis Anderss. is a good candidate for C₄ bioenergy crop development for marginal lands. As one of the characteristics of marginal lands, salinization is a major limitation to agricultural production. The present work aimed to investigate the possible factors involved in the tolerance of M. sinensis C₄ photosynthesis to salinity stress.
• Seedlings of two accessions (salt‐tolerant ‘JM0119’ and salt‐sensitive ‘JM0099’) were subjected to 0 mm NaCl (control) or 250 mm NaCl (salt stress treatment) for 2 weeks. The chlorophyll content, parameters of photosynthesis and chlorophyll a fluorescence, activity of C₄ enzymes and expression of C₄ genes were measured.
• The results showed that photosynthesis rate, transpiration rate, chlorophyll content, PSII operating efficiency, coefficient of photochemical quenching, activity of phosphoenolpyruvate carboxylase (PEPC) and pyruvate, orthophosphate dikinase (PPDK) and gene expression of PEPC and PPDK under salinity were higher after long‐term salinity exposure in ‘JM0119’ than in ‘JM0099’, while activity of NADP‐malate dehydrogenase (NADP‐MDH) and NADP‐malic enzyme (NADP‐ME), together with expression of NADP‐MDH and NADP‐ME, were much higher in ‘JM0099’ than in ‘JM0119’.
• In conclusion, the increased photosynthetic capacity under long‐term salt stress in the salt‐tolerant relative to the salt‐sensitive M. sinensis accession was mainly associated with non‐stomatal factors, such as reduced chlorophyll loss, higher PSII operating efficiency, enhanced activity of PEPC and PPDK and relatively lower activity of NADP‐ME.

     

Improving our understanding of environmental controls on the distribution of C3 and C4 grasses

A number of studies have demonstrated the ecological sorting of C₃ and C₄ grasses along temperature and moisture gradients. However, previous studies of C₃ and C₄ grass biogeography have often inadvertently compared species in different and relatively unrelated lineages, which are associated with different environmental settings and distinct adaptive traits. Such confounded comparisons of C₃ and C₄ grasses may bias our understanding of ecological sorting imposed strictly by photosynthetic pathway. Here, we used MaxEnt species distribution modeling in combination with satellite data to understand the functional diversity of C₃ and C₄ grasses by comparing both large clades and closely related sister taxa. Similar to previous work, we found that C₄ grasses showed a preference for regions with higher temperatures and lower precipitation compared with grasses using the C₃ pathway. However, air temperature differences were smaller (2 °C vs. 4 °C) and precipitation and % tree cover differences were larger (1783 mm vs. 755 mm, 21.3% vs. 7.7%, respectively) when comparing C₃ and C₄ grasses within the same clade vs. comparing all C₄ and all C₃ grasses (i.e., ignoring phylogenetic structure). These results were due to important differences in the environmental preferences of C₃ BEP and PACMAD clades (the two main grass clades). Winter precipitation was found to be more important for understanding the distribution and environmental niche of C₃ PACMADs in comparison with both C₃ BEPs and C₄ taxa, for which temperature was much more important. Results comparing closely related C₃–C₄ sister taxa supported the patterns derived from our modeling of the larger clade groupings. Our findings, which are novel in comparing the distribution and niches of clades, demonstrate that the evolutionary history of taxa is important for understanding the functional diversity of C₃ and C₄ grasses, and should have implications for how grasslands will respond to global change.     

C4 anatomy can evolve via a single developmental change

C₄ photosynthesis is a complex trait that boosts productivity in warm environments. Paradoxically, it evolved independently in numerous plant lineages, despite requiring specialised leaf anatomy. The anatomical modifications underlying C₄ evolution have previously been evaluated through interspecific comparisons, which capture numerous changes besides those needed for C₄ functionality. Here, we quantify the anatomical changes accompanying the transition between non‐C₄ and C₄ phenotypes by sampling widely across the continuum of leaf anatomical traits in the grass Alloteropsis semialata. Within this species, the only trait that is shared among and specific to C₄ individuals is an increase in vein density, driven specifically by minor vein development that yields multiple secondary effects facilitating C₄ function. For species with the necessary anatomical preconditions, developmental proliferation of veins can therefore be sufficient to produce a functional C₄ leaf anatomy, creating an evolutionary entry point to complex C₄ syndromes that can become more specialised.     

Physiological responses in two populations of Andropogon glomeratus Walter B.S.P. to short-term salinity

Summary Andropogon glomeratus is a C₄ nonhalophytic grass which exhibits population differentiation for tolerance to short-term salinity exposure. To investigate possible physiological mechanisms whch enable salt-tolerant individuals to survive short-term inundation, gas exchange and water relations parameters were measured before and during a 5-day watering treatment of half-strength synthetic seawater in plants from a tolerant and a non-tolerant population. Photosynthetic recovery was followed for 10 days after the salinity treatment. Photosynthetic CO₂ uptake was substantially inhibited in both populations. Stomatal conductances decreased and intercellular CO₂ concentrations increased, indicating non-stomatal factors were primarily responsible for the decrease in CO₂ uptake. After termination of the salinity treatment photosynthetic capacity increased more rapidly in the tolerant population and reached the pretreatment level after 6 days, whereas the nontolerant population did not recover fully after 10 days. A-Ci curves measured before and after the salinity treatment indicated a decrease in the carboxylation efficiency, and suggested a proportionately greater metabolic inhibition relative to the increase in the stomatal limitation. Osmotic adjustment occurred in a 2-day period in the tolerant population, but there was no change in the osmotic potentials or the water potential at the point of turgor loss in the nontolerant population. Thus short-term salt tolerance in the marsh population is associated with rapid osmotic adjustment and recovcry of photosynthetic capacity shortly after the end of the salinity exposure, rather than maintenance of greater photosynthesis during the salinity treatment.     

C4 Photosynthesis evolved in grasses via parallel adaptive genetic changes

Phenotypic convergence is a widespread and well-recognized evolutionary phenomenon. However, the responsible molecular mechanisms remain often unknown mainly because the genes involved are not identified. A well-known example of physiological convergence is the C4 photosynthetic pathway, which evolved independently more than 45 times [1]. Here, we address the question of the molecular bases of the C4 convergent phenotypes in grasses (Poaceae) by reconstructing the evolutionary history of genes encoding a C4 key enzyme, the phosphoenolpyruvate carboxylase (PEPC). PEPC genes belong to a multigene family encoding distinct isoforms of which only one is involved in C4 photosynthesis [2]. By using phylogenetic analyses, we showed that grass C4 PEPCs appeared at least eight times independently from the same non-C4 PEPC. Twenty-one amino acids evolved under positive selection and converged to similar or identical amino acids in most of the grass C4 PEPC lineages. This is the first record of such a high level of molecular convergent evolution, illustrating the repeatability of evolution. These amino acids were responsible for a strong phylogenetic bias grouping all C4 PEPCs together. The C4-specific amino acids detected must be essential for C4 PEPC enzymatic characteristics, and their identification opens new avenues for the engineering of the C4 pathway in crops.     

C4 Photosynthesis Promoted Species Diversification during the Miocene Grassland Expansion

Identifying how organismal attributes and environmental change affect lineage diversification is essential to our understanding of biodiversity. With the largest phylogeny yet compiled for grasses, we present an example of a key physiological innovation that promoted high diversification rates. C₄ photosynthesis, a complex suite of traits that improves photosynthetic efficiency under conditions of drought, high temperatures, and low atmospheric CO₂, has evolved repeatedly in one lineage of grasses and was consistently associated with elevated diversification rates. In most cases there was a significant lag time between the origin of the pathway and subsequent radiations, suggesting that the ‘C₄ effect’ is complex and derives from the interplay of the C₄ syndrome with other factors. We also identified comparable radiations occurring during the same time period in C₃ Pooid grasses, a diverse, cold-adapted grassland lineage that has never evolved C₄ photosynthesis. The mid to late Miocene was an especially important period of both C₃ and C₄ grass diversification, coincident with the global development of extensive, open biomes in both warm and cool climates. As is likely true for most “key innovations”, the C₄ effect is context dependent and only relevant within a particular organismal background and when particular ecological opportunities became available.     

Climate, phylogeny and the ecological distribution of C4 grasses

'C4 photosynthesis' refers to a suite of traits that increase photosynthesis in high light and high temperature environments. Most C4 plants are grasses, which dominate tropical and subtropical grasslands and savannas but are conspicuously absent from cold growing season climates. Physiological attributes of C4 photosynthesis have been invoked to explain C4 grass biogeography; however, the pathway evolved exclusively in grass lineages of tropical origin, suggesting that the prevalence of C4 grasses in warm climates could be due to other traits inherited from their non-C4 ancestors. Here we investigate the relative influences of phylogeny and photosynthetic pathway in determining the ecological distributions of C4 grasses in Hawaii. We find that the restriction of C4 grasses to warmer areas is due largely to their evolutionary history as members of a warm-climate grass clade, but that the pathway does appear to confer a competitive advantage to grasses in more arid environments.     

Variations in nitrogen use efficiency reflect the biochemical subtype while variations in water use efficiency reflect the evolutionary lineage of C4 grasses at inter‐glacial CO2

C₄ photosynthesis evolved multiple times in diverse lineages. Most physiological studies comparing C₄ plants were not conducted at the low atmospheric CO₂ prevailing during their evolution. Here, 24 C₄ grasses belonging to three biochemical subtypes [nicotinamide adenine dinucleotide malic enzyme (NAD‐ME), phosphoenolpyruvate carboxykinase (PCK) and nicotinamide adenine dinucleotide phosphate malic enzyme (NADP‐ME)] and six major evolutionary lineages were grown under ambient (400 μL L^?1) and inter‐glacial (280 μL L^?1) CO₂. We hypothesized that nitrogen‐related and water‐related physiological traits are associated with subtypes and lineages, respectively. Photosynthetic rate and stomatal conductance were constrained by the shared lineage, while variation in leaf mass per area (LMA), leaf N per area, plant dry mass and plant water use efficiency were influenced by the subtype. Subtype and lineage were equally important for explaining variations in photosynthetic nitrogen use efficiency (PNUE) and photosynthetic water use efficiency (PWUE). CO₂ treatment impacted most parameters. Overall, higher LMA and leaf N distinguished the Chloridoideae/NAD‐ME group, while NADP‐ME and PCK grasses were distinguished by higher PNUE regardless of lineage. Plants were characterized by high photosynthesis and PWUE when grown at ambient CO₂ and by high conductance at inter‐glacial CO₂. In conclusion, the evolutionary and biochemical diversity among C₄ grasses was aligned with discernible leaf physiology, but it remains unknown whether these traits represent ecophysiological adaptation.     

Transcriptome Analysis of the Heritable Salt Tolerance of Prairie Cordgrass (<Emphasis Type="Italic">Spartina pectinata Link</Emphasis>)

The salt-tolerant capability of the candidate bioenergy crop prairie cordgrass greatly surpasses that of previously characterized prairie grass species and most other plants. To understand the mechanism of inherited salt tolerance, we compared phenotypic and genetic qualities in half-sib families of prairie cordgrass after salt treatment. Each family was treated with a 400 mM NaCl solution or a water control and then measured for various health phenotypes. Phenotypes associated with salt tolerance were shown to be moderately heritable between parent and offspring. RNA-seq analysis revealed differential regulation in unique pathways including metabolism, signaling, photosynthesis, and the circadian rhythm. The studies herein suggest that alternative regulation of the photosynthetic pathway could confer increased salt resistance in halophytes and can be monitored phenotypically or genetically in breeding programs. The improvement of salt-tolerant traits in prairie cordgrass would increase its potential to be grown as a bioenergy crop on lands that are not suitable for the growth of food crops.     

Evolution and ecology of seed internal morphology in relation to germination characteristics in Amaranthaceae

Background and AimsInternal seed morphological traits such as embryo characteristics and nutritive tissue can vary considerably within a plant lineage. These traits play a prominent role in germination processes and the success of seedling establishment, and are therefore under high selective pressure, especially in environments hostile to seedlings, such as arid, saline or highly dynamic habitats. We investigated the relationships of seed internal morphology and germination characteristics of 84 species of Amaranthaceae s.l., a family with numerous lineages that have adapted to stressful growing conditions.MethodsWe used seed cross-sections to assess embryo type and the ratios of embryo to seed surface and radicle to cotyledon length. Furthermore, seed mass, mean time to germination, habitat preferences and further plant traits such as C₃ or C₄ photosynthesis and life form were compiled for each species. Data were analysed using phylogenetic comparative methods.Key resultsWe found embryo type (λ = 1), log seed mass (λ = 0.86) and the ratio of embryo to seed size (λ = 0.78) to be evolutionarily stable, with an annular embryo as ancestral in the family. Linked to shifts to the three derived embryos types (spiral, horseshoe-shaped and curved) is an increase in the ratio of root to cotyledon length and a reduction of nutritive tissue. We observed stabilizing selection towards seeds with relatively large embryos with longer radicles and less nutritive tissue that are able to germinate faster, especially in lineages with C₄ photosynthesis and/or salt tolerance.ConclusionsWe conclude that the evolutionary shift of nutrient storage from perisperm to embryo provides an ecological advantage in extreme environments, because it enables faster germination and seedling establishment. Furthermore, the evolutionary shift towards a higher ratio of root to cotyledon length especially in small-seeded Amaranthaceae growing in saline habitats can provide an ecological advantage for fast seedling establishment.     

Global grass (Poaceae) success underpinned by traits facilitating colonization,persistence and habitat transformation

Poaceae (the grasses) is arguably the most successful plant family, in terms of its global occurrence in (almost) all ecosystems with angiosperms, its ecological dominance in many ecosystems, and high species richness. We suggest that the success of grasses is best understood in context of their capacity to colonize, persist, and transform environments (the “Viking syndrome”). This results from combining effective long‐distance dispersal, efficacious establishment biology, ecological flexibility, resilience to disturbance and the capacity to modify environments by changing the nature of fire and mammalian herbivory. We identify a diverse set of functional traits linked to dispersal, establishment and competitive abilities. Enhanced long‐distance dispersal is determined by anemochory, epizoochory and endozoochory and is facilitated via the spikelet (and especially the awned lemma) which functions as the dispersal unit. Establishment success could be a consequence of the precocious embryo and large starch reserves, which may underpin the extremely short generation times in grasses. Post‐establishment genetic bottlenecks may be mitigated by wind pollination and the widespread occurrence of polyploidy, in combination with gametic self‐incompatibility. The ecological competitiveness of grasses is corroborated by their dominance across the range of environmental extremes tolerated by angiosperms, facilitated by both C₃ and C₄ photosynthesis, well‐developed frost tolerance in several clades, and a sympodial growth form that enabled the evolution of both annual and long‐lived life forms. Finally, absence of investment in wood (except in bamboos), and the presence of persistent buds at or below ground level, provides tolerance of repeated defoliation (whether by fire, frost, drought or herbivores). Biotic modification of environments via feedbacks with herbivory or fire reinforce grass dominance leading to open ecosystems. Grasses can be both palatable and productive, fostering high biomass and diversity of mammalian herbivores. Many grasses have a suite of architectural and functional traits that facilitate frequent fire, including a tufted growth form, and tannin‐like substances in leaves which slow decomposition. We mapped these traits over the phylogeny of the Poales, spanning the grasses and their relatives, and demonstrated the accumulation of traits since monocots originated in the mid‐Cretaceous. Although the sympodial growth form is a monocot trait, tillering resulting in the tufted growth form most likely evolved within the grasses. Similarly, although an ovary apparently constructed of a single carpel evolved in the most recent grass ancestor, spikelets and the awned lemma dispersal units evolved within the grasses. Frost tolerance and C₄ photosynthesis evolved relatively late (late Palaeogene), and the last significant trait to evolve was probably the production of tannins, associated with pyrophytic savannas. This fits palaeobotanical data, suggesting several phases in the grass success story: from a late Cretaceous origin, to occasional tropical grassland patches in the later Palaeogene, to extensive C₃ grassy woodlands in the early–middle Miocene, to the dramatic expansion of the tropical C₄ grass savannas and grasslands in the Pliocene, and the C₃ steppe grasslands during the Pleistocene glacial periods. Modern grasslands depend heavily on strongly seasonal climates, making them sensitive to climate change.     

Photosynthetic carbon metabolism of the cool-temperate C4 grass Spartina anglica Hubb.

The aim of this work was to describe the photosynthetic carbon metabolism of the cooltemperate C₄ grass Spartina anglica. With the exception of pyruvate, phosphate dikinase and pyruvate kinase, the maximum catalytic activities in leaves of putative enzymes of the C₄ cycle of a phosphoenolpyruvate-carboxykinase C₄ plant were considerably in excess of the observed, steady-state rate of photosynthesis, and were comparable with the maximum catalytic activities of key enzymes of the reductive pentose-phosphate pathway. Radioactive carbon from ¹⁴CO₂ supplied to attached leaves during steady-state photosynthesis appeared first in malate and aspartate from which it moved to intermediates of the reductive pentose-phosphate pathway, and then to sucrose. These experiments show that photosynthetic carbon metabolism in this cool-temperate C₄ plant is similar to that of C₄ plants of hotter climates.     

Molecular phylogeny of Flaveria as deduced from the analysis of nucleotide sequences encoding the H-protein of the glycine cleavage system

Sequence comparisons have shown that nucleotide sequences of the H-protein, a component of the glycine cleavage system, are only moderately conserved and can be used as molecular markers for intrageneric phylogenetic studies. We have analysed the respective cDNA sequences from 12 species of Flaveria, and a more limited set of gdcsH upstream regions. These data are discussed with respect to a phylogenetic reconstruction of Flaveria, a small genus which includes species of different photo-synthetic types, namely C₃, C₃-C₄, C₄-like and C₄. Our analysis essentially supports an earlier hypothesis, based on morphological and eco-geographical data, of the evolution of Flaveria (Powell 1978). This close agreement shows the usefulness of H-protein nucleotide sequences at a low taxonomic level. Our analysis independently confirms that C₄ photosynthesis has evolved two times in different lineages of Flaveria. Most remarkably, the C₄ taxa of Flaveria appear as derived relative to the C₃-C₄ intermediate taxa, i.e. they probably have common direct predecessors. This is the first direct evidence for a phylo-genetically intermediate position of C₃-C₄ intermediate photosynthesis. Our data also confirm the antiquity of C₃ photosynthesis in Flaveria but suggest that the collection of F.pringlei used in our experiments, although clearly of C₃ photosynthetic metabolism, possibly originated from hybridization with a more advanced taxon.     

Ecological selection pressures for C4 photosynthesis in the grasses

Grasses using the C₄ photosynthetic pathway dominate grasslands and savannahs of warm regions, and account for half of the species in this ecologically and economically important plant family. The C₄ pathway increases the potential for high rates of photosynthesis, particularly at high irradiance, and raises water-use efficiency compared with the C₃ type. It is therefore classically viewed as an adaptation to open, arid conditions. Here, we test this adaptive hypothesis using the comparative method, analysing habitat data for 117 genera of grasses, representing 15 C₄ lineages. The evidence from our three complementary analyses is consistent with the hypothesis that evolutionary selection for C₄ photosynthesis requires open environments, but we find an equal likelihood of C₄ evolutionary origins in mesic, arid and saline habitats. However, once the pathway has arisen, evolutionary transitions into arid habitats occur at higher rates in C₄ than C₃ clades. Extant C₄ genera therefore occupy a wider range of drier habitats than their C₃ counterparts because the C₄ pathway represents a pre-adaptation to arid conditions. Our analyses warn against evolutionary inferences based solely upon the high occurrence of extant C₄ species in dry habitats, and provide a novel interpretation of this classic ecological association.     

The C(4) plant lineages of planet Earth

Using isotopic screens, phylogenetic assessments, and 45 years of physiological data, it is now possible to identify most of the evolutionary lineages expressing the C(4) photosynthetic pathway. Here, 62 recognizable lineages of C(4) photosynthesis are listed. Thirty-six lineages (60%) occur in the eudicots. Monocots account for 26 lineages, with a minimum of 18 lineages being present in the grass family and six in the sedge family. Species exhibiting the C(3)-C(4) intermediate type of photosynthesis correspond to 21 lineages. Of these, 9 are not immediately associated with any C(4) lineage, indicating that they did not share common C(3)-C(4) ancestors with C(4) species and are instead an independent line. The geographic centre of origin for 47 of the lineages could be estimated. These centres tend to cluster in areas corresponding to what are now arid to semi-arid regions of southwestern North America, south-central South America, central Asia, northeastern and southern Africa, and inland Australia. With 62 independent lineages, C(4) photosynthesis has to be considered one of the most convergent of the complex evolutionary phenomena on planet Earth, and is thus an outstanding system to study the mechanisms of evolutionary adaptation.