Related interest:

Paleobiology
Stromatolites
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.

After 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 and 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.