Kingdom Plantae

Tree of Life

Plant Kingdom

Related interest:


Plant Fossils Gallery

Green River Plant Fossils

Evolution of Plants:

The chloroplasts of green plants are surrounded by two membranes, supporting the theory of an endosymbiosis, with cyanobacteria a common ancestor. Embryophytes descended from green algae during the Palaeozoic era, and are also called the land plants (though some live in water) and include all the trees, flowers, ferns, mosses with which we are all familiar. All are complex multicellular organisms with specialized reproductive organs and, with rare exception, use photosynthesis for their energy.

For some 1.5 billion years, photosynthetic organisms remained in the sea, protected from ultraviolent radiation. The earliest photosynthetic organisms to invade land probably resembled modern algae, cyanobacteria, and lichens, and were followed by the bryophyte, including liverworts (Division Marchantiophyta) and mosses (Division Bryophyta) that descended from the charophyte group of green algae.

Bryophites in fossil amberAfter evolving from primitive green algae, plants probably began their terrestrial invasion some 450 million years ago during the late Ordovician, with a first major evolutionary task being desiccation resistance. Vascular structures emerged to transport water and nutrients to tissue that was above the water. Symbiotic relationships with fungi emerged to assist in the uptake of nutrients from moist soil, as opposed to flooded soil. Later success was fostered by the evolution of means for gamete andSilurian Cooksonia progeny dispersal in flowers and seeds among some, but not all, plant lineages.

Land colonization by plants is believed to have been achieved by around 425 Ma during the Silurian with the appearance of the vascular plants. Cooksonia is usually considered the earliest fossil of a vascular land plant; it was a small plant, only a few centimeters high. Its leafless stems had sporangia (spore-producing structures) at their tips. No specimen has been found with roots suggesting it connected to the ground with very fine root hairs.

As plants evolved and spread across terrestrial landscapes, and themselves adapted to changing environments, they were a major selective influence in paleobiology and evolution of animals (co-evolution) from the time of their prominence in the Paleozoic, and through the Mesozoic and Cenozoic. Gymnosperms, and especially the cycads, were the dominant land plants in the Jurassic, but the Cretaceous saw the rise of the flowering plants (angiosperms) and their associated insect pollinators (an example of co-evolution) became the dominant plant form that continues to present day.

The fossil record has been ambiguous since the time of Darwin as to when and from what ancestors flowing plants arose. The oldest undisputed flowing plant fossil dates to 125 million years ago in the Cretaceous. However, modern genome sequencing of plants with apparent primitive phenotypes and other evidence suggest that the angiosperm lineage may begin with or near a ginkgo-like plant from Liaoning China, Schmeissneria, in the early to middle Jurassic (Wing, 2007). This origin is but one of many competing hypotheses, but at present, there exists some consensus that one or perhaps two whole genome duplications in angiosperm ancestors enabled the evolutionary leap to flowers, altering the earth and its ecosystems forever thereafter.

About Plants

In the most general context, plants are at the bottom of the majority of terrestrial food chains, and through photosynthesis, produce the energy for most of earth’s life, directly or indirectly. Most oxygen essential for we eukaryotes come from plants as their metabolic byproduct. The amphibians followed the "amphibious" plants onto land, as did the reptiles follow plants onto land. Interestingly, the rise of mammals coincided with the rise of plants that, like mammals, utilize internal development by enclosing embryos in a protective and nourishing shell, the seed in the case of plants. The number of plant species on earth can only be estimated, and is believed to exceed three hundred thousand (far and away mainly flowing plants), albeit, only a limited number is suitable for domestication and human food consumption.

Plant Evolution - Kingdom Plantae Classification Systematics and Phylogeny

Kingdom Plantae classification, systematics and phylogeny are not settled science, and the tree of life for plants has undergone major revisions in recent years. There are many competing views and hypotheses, with more revisions the assured outcome. Unraveling the mysteries of plant evolution is being made possible by now very inexpensive molecular whole genome sequencing across the plant Kingdom. The history of plant life is all pretty confusing, so we've tried to condense it in the table below, and provide succinct supporting summaries in the table notes.

Viridiplantae or Green Plants

Unranked Groups or Subkingdoms
Green Algae (Fomerly in now obsolete Kingdom Protista - see note 2)  Chlorophyta
Unranked Embryophytes (Land Plants) - see note 1
Bryophytes (Non-Vascular plants) Marchantiophyta - liverworts
Anthocerotophyta - hornworts
Bryophyta - mosses
 Unranked Tracheophytes (Vascular Plants - note 2) Non-seed-bearing plants Rhyniophyta - rhyniophytes
Zosterophyllophyta - zosterophylls
Lycopodiophyta - clubmosses
Trimerophytophyta trimerophytes
Pteridophyta - true ferns and horsetails
Progymnospermophyta - whisk ferns
Unranked Spermatophytes (seed plants - note 3) Gymnosperm (note 4) Pteridospermatophyta - seed ferns
Gymnosperms Gymnospermae (notes 4 and 5) Pinophyta - conifers
Cycadophyta - cycads
Ginkgophyta - ginkgo
Gnetophyta - gnetae
Angiosperms - flowering plants (notes 4 and 5) Magnoliophyta - flowering plants (also called angiosperms, angiospermopsida)
  1. Importantly, the embryophytes (or land plants) are believed to have evolved from Charophyte green algae. Green algae and the embryophytes together comprise the clade Viridiplantae (often referred to simply as the green plants). Viridiplantae are united by cells with cellulose providing structure, and with cellular metabolic machinary having chloroplasts evolved from endosymbiosis with cyanobacteria. Endosymbiosis is a well-supported theory explaining the evolution of chloroplasts (in plants) and mitochondria (in animals) in eukaryotic cells; in the simplest terms, primitive eukaryotic cells hijacked photosynthetic prokaryotic cells (probably proteobacteria eventually leading to animal mitochondria and cyanobacteria leading eventually plant plastids), fed them, and used their photosynthetic metabolic machinery to produce their energy aerobically, burning oxygen and respiring carbon dioxide in the process. Estimated very wildly, but the seminal endosymbiotic event is often hypothesized to have occured in Proterozoic between 2000 and 1500 million years ago.
  2. Algae were once considered to be in now obsolete Kingdom Protista rather than Kingdom Plantae. There are several different groups of algal organisms that are predominently photosynthetic. Most notable are seaweeds that are multicellular algae and appear much like land plants, but are classified separately as brown algae. Red multicellular algae is also no longer contained in Plantae.
  3. Phylogeny for modern Spermatophyta (seed plants) and some related vascular plant groups is shown to the right (click the image to enlarge). The spore-bearing vascular plants are paraphyletic with respect to the seed plants, with ferns (Pteridophyta) more closely related to seed plants than they are to clubmosses (Lycopodiophyta)
  4. Seed plants span the fossil record with the seed ferns, or (Pteridospermae) once dominating and building entire forests especially in the Upper Paleozoic. By the Triassic period, seed ferns were largely replaced by gymnosperms until the Cretaceous, when the Angiosperms became dominant, and underwent a massive diversity radiation.
  5. Gymnosperm (Gymnospermae) is a name derived from the Greek word for naked seed. They comprise a group of seed-bearing and hence vascular plants whose seeds appear “naked” on scales of a cone or, as opposed being formed within an ovule and developing fruit, as is the case for the angiosperms. The Pteridospermatophyta, or seed ferns, is an extinct gymnosperm division that were predominant in the Devonian. The systematic position of the Pteridospermatophyta is currently in debate.
  6. The angiosperms are the vast and major group of flowering plants whose seeds are covered in a true fruit. The reproductive organs are in a flower and the ovule is enclosed within a carpel that will lead to a fruit.

Also see:

Representative Plant Fossils Across Geological Time


  • Davies, T. J. (2004). "Darwin's abominable mystery: Insights from a supertree of the angiosperms". Proceedings of the National Academy of Sciences 101 (7): 1904–9.
  • Jiao, Yuannian; Wickett, No4rman J.; Ayyampalayam, Saravanaraj; Chanderbali, André S.; et al. (2011). "Ancestral polyploidy in seed plants and angiosperms". Nature 473 (7345): 97–100
  • De Bodt, S., Maere, S. & Van de Peer, Y. Genome duplication and the origin of angiosperms. Trends Ecol. Evol. 20, 591–597 (2005)
  • Soltis, D. E., Bell, C. D., Kim, S. & Soltis, P. S. Origin and early evolution of angiosperms. Ann. NY Acad. Sci. 1133, 3–25 (2008)
  • Fawcett, J. A., Maere, S. & Van de Peer, Y. Plants with double genomes might have had a better chance to survive the Cretaceous-Tertiary extinction event. Proc. Natl Acad. Sci. USA 106, 5737–5742 (2009)
  • Keith Adams (December 2013). "Genomic Clues to the Ancestral Flowering Plant". Science 342 (6165): 1456–1457
  • Xin Wing; Shuying Duan, Baoyin Geng, Jinzhong Cui and Yong Yang (2007). "Schmeissneria: A missing link to angiosperms?". BMC Evolutionary Biology 7: 14.