Paleobotany is important in the reconstruction of ancient ecological systems and climate, known as paleoecology and paleoclimatology respectively; and is fundamental to the study of green plant development and evolution. Paleobotany has also become important to the field of archaeology, primarily for the use of phytoliths in relative dating and in paleoethnobotany,
An important early land plant fossil locality is the Rhynie Chert, an Early Devonian sinter (hot spring) deposit composed primarily of silica found outside the town of Rhynie in Scotland. The Rhynie Chert is exceptional due to its preservation of several different clades of plants, from mosses and lycopods to more unusual, problematic forms. Many fossil animals, including arthropods and arachnids, are also found in the Rhynie Chert, and it offers a unique window on the history of early terrestrial life.
Plant-derived macrofossils become abundant in the Late Devonian and include tree trunks, fronds, and roots. The earliest tree is Archaeopteris, which bears simple, fern-like leaves spirally arranged on branches atop a conifer-like trunk (Meyer-Berthaud et al., 1999).
Widespread coal swamp deposits across North America and Europe during the Carboniferous Period contain a wealth of fossils containing arborescent lycopods up to 30 meters tall, abundant seed plants, such as conifers and seed ferns, and countless smaller, herbaceous plants.
One of the most common kinds of plant fossils is a compression fossil, in which a leaf or flattened part of the plant has been pressed between layers of sediment and often preserved as a carbonaceous film. Also common are fossil pollen and spores from ancient lake beds, as well as charcoal. Less common, but economically more important, is coal from the plants of Carboniferous swamps.
One of the most spectacular of plant fossils is petrified wood.
Since a leaf, stem, spore, or seed may be found preserved without any physical connection to the plant from which it came, paleobotanists use form taxa (singular form taxon) to name and classify such fossils. When the true identity of such fossils is later discovered, the two form taxa may be merged. For example, in the 1960s fossil leaves called Archaeopteris (literally "ancient fern") were found attached to fossil wood of the tree Callixylon. The whole plant is now known to be a Devonian tree with fern-like leaves but with gymnosperm-like wood.
Some form taxa continue to exist even after their identity is determined. This is a matter of convenience for identifying quickly which part was found as a fossil, especially which the fossil may come from more than one kind of plant. Leaves assigned to the form taxon Sphenopteris come from both ferns and from seed plants; it usually is not possible to determine from isolated fossils which group the leaves belong to.
Some plants have remained remarkedly unchanged throughout earth's geological time scale. Early ferns had developed by the Mississippian, conifers by the Pennsylvanian. Some plants of prehistory are the same ones around today and are thus living fossils, such as Ginkgo biloba and Sciadopitys verticillata. Other plants have changed radically, or have gone extinct entirely.
A few examples of prehistoric plants are: