Evolution of Land Plants
- LAST REVIEWED: 19 January 2021
- LAST MODIFIED: 24 April 2019
- DOI: 10.1093/obo/9780199941728-0119
- LAST REVIEWED: 19 January 2021
- LAST MODIFIED: 24 April 2019
- DOI: 10.1093/obo/9780199941728-0119
The colonization of land by plants was one of the most important events in the earth’s history, setting the stage for the greening of the continents, increased oxygenation of the atmosphere, and the provision of food and habitat for the animals and microorganisms that evolved in parallel—and in many cases, diversified in their shadows. They are the foundation of agriculture and the source of timber, fibers, pharmaceuticals, and psychoactives. Fossilized plants, in particular, drive our global economy, being the source of coal, petroleum, and natural gas. And living plants represent huge above- and below-ground (as roots and microalgae) carbon sinks. Continental colonists who appeared before land plants (embryophytes) included prokaryotic microbes, eukaryotic microalgae, and fungi. The conditions necessary for colonization—sufficient areas of stable land accessible to marine and aquatic organisms, formation of soils, and equable atmospheric and climatic conditions—appear to have been established approximately 540–440 million years ago (MA; Cambrian and Ordovician). By about 470–460 MA (middle Ordovician), plant microfossils first appear in the fossil record, including spores, cuticular fragments, and tracheid cells. Early plant micro- and macrofossils, when considered together, displayed adaptations that facilitated survival on land, including coatings to reduce desiccation, stomata to facilitate gas exchange (in all lineages but liverworts), and specialized cells such as tracheids for the movement of water and nutrients (precursors of a vascular system). By about 410 MA (late Silurian to early Devonian), vegetation comprising small plants with a well-developed vascular system was establishing itself on multiple continents. From about 390–360 MA (middle to late Devonian), the number of species increased rapidly, and by 360 MA the major extant lineages of land plants were established. Major innovations in plant form began to appear, including the capacity to attain great height and size, and in the late Devonian period, the evolution of seeds. The seed provided protection during periods of dormancy and facilitated survival at greater distances from water. These events were followed during the Cretaceous/Cenozoic by one of the most spectacular radiations of any terrestrial clade: the rise of the angiosperms, which in the 21st century constitute about 90 percent of all land plant diversity.
Today’s flora has been assembled from just ten major living lineages or clades (a branch in the phylogeny that includes an ancestor and all its descendants). These are: three clades of non-vascular plants (liverworts, mosses, and hornworts [collectively, the bryophytes]); and seven clades of vascular plants, two of which are free-sporing, or lacking in seeds (lycophytes and ferns); and five of which are seed-bearing (cycads, ginkgo, conifers, gnetophytes [collectively, gymnosperms], and angiosperms). Diversification into all of these clades except the angiosperms had occurred by about 360 MA (Bell and Hemsley 2000). Gymnosperms in particular were previously much more numerous; up to 70 percent of their major lineages became extinct after the origin of angiosperms (Friis, et al. 1987). All land plants share the characteristic that they produce two distinct multicellular structures, a haploid gamete-bearing plant (gametophyte) and a diploid spore-bearing plant (sporophyte). Multicellular gametophytes are shared with their algal relatives, but multicellular sporophytes are a hallmark of land plants. The earliest land plants were relatively simple in form, and paleo- and neobotanical evidence suggests that they resembled mosslike plants (Willis and McElwain 2014). Cellular differentiation of both vegetative and reproductive structures was limited, and they lacked leaves, roots, and seeds. Their size was restricted by the lack of strengthening tissue and a vascular system to conduct water and nutrients. Living members of the earliest diverging lineages of land plants (byrophytes) mostly retain this simplicity and small size. A key feature of bryophytes is the predominance of the gametophytic stage of the life cycle and the dependence of the smaller, more ephemeral sporophytes on the gametophyte. In vascular plants (tracheophytes), on the other hand, branched sporophytes live independently from the much smaller and often ephemeral gametophytes. This evolutionary progression from a dominant haploid phase in the earliest land plants to a dominant diploid phase in vascular plants is a key theme of land plant evolution (Kenrick 2017). The origin of sporophytic dominance has been explained by two debated hypotheses: the homologous and the antithetic (or intercalary) hypotheses (Kenrick and Crane 1997). The first proposes that the ancestral sporophyte and gametophyte were morphologically similar and have since diverged. The second invokes the novel origin of a multicellular sporophyte that resulted from a delay of meiosis coupled with mitotic divisions in the zygote, producing an embryonic sporophyte retained by, and dependent on, the larger gametophyte. The following sections list key texts or focus on the evolution, diversity, and global impacts of land plants.
Bell, Peter R., and Alan R. Hemsley. 2000. Green plants. Their origin and diversity. 2d ed. Cambridge, UK: Cambridge Univ. Press.
A broad survey of the diversity of both living and extinct plant taxa.
Friis, Else M., William G. Chaloner, and Peter R. Crane, eds. 1987. The origins of angiosperms and their biological consequences. New York: Cambridge Univ. Press.
A collection of chapters focusing on the origin of angiosperms and changes in the earth’s flora and fauna during the development of angiosperm-dominated plant communities.
Kenrick, Paul. 2017. Changing expressions: A hypothesis for the origin of the vascular plant life cycle. Philosophical Transactions of the Royal Society of London B 373:20170149.
An important article that synthesizes evidence from fossils of the Rhynie chert with advances in developmental genetics and plant phylogenetics, focusing on different hypotheses explaining the free-living sporophyte of vascular plants and highlighting the importance of this transition in the subsequent evolution of land plants.
Kenrick, Paul., and Peter R. Crane. 1997. The origin and early diversification of land plants: A cladistic study. Washington, DC: Smithsonian Institution Press.
An exceptional and comprehensive study of mostly macrofossil evidence on origins and early diversification of land plants. Also discusses historical theories on the origin of land plants. It is a valuable source of information on both living and extinct plants, and on their traits and evolution. Data were amassed from macrofossils and living plants for cladistic analyses to clarify relationships among major groups of land plants except seed plants.
Willis, Katherine J., and Jennifer C. McElwain. 2014. The evolution of plants. Oxford: Oxford Univ. Press.
A broad survey of the diversity of both living and extinct plant taxa with a phylogenetic focus.
- Adaptive Radiation
- Ancient DNA
- Behavioral Ecology
- Canalization and Robustness
- Character Displacement
- Cognition, Evolution of
- Constraints, Evolutionary
- Contemporary Evolution
- Convergent Evolution
- Cooperation and Conflict: Microbes to Humans
- Cooperative Breeding in Insects and Vertebrates
- Cryptic Female Choice
- Darwin, Charles
- Disease Virulence, Evolution of
- Ecological Speciation
- Epigenetics and Behavior
- Epistasis and Evolution
- Eusocial Insects as a Model for Understanding Altruism, Co...
- Evidence of Evolution, The
- Evolution and Development: Genes and Mutations Underlying ...
- Evolution and Development of Individual Behavioral Variati...
- Evolution, Cultural
- Evolution of Animal Mating Systems
- Evolution of Antibiotic Resistance
- Evolution of New Genes
- Evolution of Plant Mating Systems
- Evolution of Specialization
- Evolutionary Biology of Aging
- Evolutionary Biomechanics
- Evolutionary Computation
- Evolutionary Developmental Biology
- Evolutionary Ecology of Communities
- Experimental Evolution
- Field Studies of Natural Selection
- Founder Effect Speciation
- Frequency-Dependent Selection
- Fungi, Evolution of
- Gene Duplication
- Gene Expression, Evolution of
- Gene Flow
- Genetics, Ecological
- Genome Evolution
- Geographic Variation
- Group Selection
- History of Evolutionary Thought, 1860–1925
- History of Evolutionary Thought before Darwin
- History of Evolutionary Thought Since 1930
- Human Behavioral Ecology
- Human Evolution
- Hybrid Speciation
- Hybrid Zones
- Identifying the Genomic Basis Underlying Phenotypic Variat...
- Inbreeding and Inbreeding Depression
- Inclusive Fitness
- Innovation, Evolutionary
- Islands as Evolutionary Laboratories
- Kin Selection
- Land Plants, Evolution of
- Landscape Genetics
- Landscapes, Adaptive
- Language, Evolution of
- Macroevolutionary Rates
- Male-Male Competition
- Mass Extinction
- Mate Choice
- Maternal Effects
- Medicine, Evolutionary
- Meiotic Drive
- Modern Synthesis, The
- Molecular Clocks
- Molecular Phylogenetics
- Mutation Rate and Spectrum
- Mutualism, Evolution of
- Natural Selection in Human Populations
- Natural Selection in the Genome, Detecting
- Neutral Theory
- New Zealand, Evolutionary Biogeography of
- Niche Construction
- Niche Evolution
- Non-Human Animals, Cultural Evolution in
- Origin and Early Evolution of Animals
- Origin of Eukaryotes
- Origin of Life, The
- Paradox of Sex
- Parental Care, Evolution of
- Personality Differences, Evolution of
- Phenotypic Plasticity
- Phylogenetic Comparative Methods and Tests of Macroevoluti...
- Phylogenetic Trees, Interpretation of
- Polyploid Speciation
- Population Genetics
- Population Structure
- Post-Copulatory Sexual Selection
- Psychology, Evolutionary
- Punctuated Equilibria
- Quantitative Genetic Variation and Heritability
- Reaction Norms, Evolution of
- Reproductive Proteins, Evolution of
- Selection, Directional
- Selection, Disruptive
- Selection Gradients
- Selection, Natural
- Selection, Sexual
- Selfish Genes
- Sexual Conflict
- Sexual Selection and Speciation
- Sexual Size Dimorphism
- Speciation Genetics and Genomics
- Speciation, Sympatric
- Species Concepts
- Sperm Competition
- Systems Biology
- Taxonomy and Classification
- Tetrapod Evolution
- The Philosophy of Evolutionary Biology
- Trends, Evolutionary
- Wallace, Alfred Russel