Phytogeography (from Greek phyto = plant and geography meaning also distribution) is the branch of biogeography that is concerned with the geographic distribution of plant species and their influence on the earth's surface. Phytogeography is concerned with all aspects of plant distribution, from the controls on the distribution of individual species ranges (at both large and small scales, see species distribution) to the factors that govern the composition of entire communities and floras. Geobotany, by contrast, focuses on the geographic space's influence on plants.
The basic data elements of phytogeography are occurrence records (presence or absence of a species) with operational geographic units such as political units or geographical coordinates. These data are often used to construct phytogeographic provinces (floristic provinces) and elements.
The questions and approaches in phytogeography are largely shared with zoogeography, except zoogeography is concerned with animal distribution rather than plant distribution. The term phytogeography itself suggests a broad meaning. How the term is actually applied by practicing scientists is apparent in the way periodicals use the term. The American Journal of Botany, a monthly primary research journal, frequently publishes a section titled "Systematics, Phytogeography, and Evolution." Topics covered in the American Journal of Botany's "Systematics and Phytogeography" section include phylogeography, distribution of genetic variation and, historical biogeography, and general plant species distribution patterns. Biodiversity patterns are not heavily covered.
Phytogeography has a long history. One of the subjects earliest proponents was Prussian naturalist Alexander von Humboldt, who is often referred to as the "father of phytogeography". Von Humboldt advocated a quantitative approach to phytogeography that has characterized modern plant geography.
Gross patterns of the distribution of plants became apparent early on in the study of plant geography. For example, Alfred Russel Wallace, co-discoverer of the principle of natural selection, discussed the Latitudinal gradients in species diversity, a pattern observed in other organisms as well. Much research effort in plant geography has since then been devoted to understanding this pattern and describing it in more detail.
In 1890, the United States Congress passed an act that appropriated funds to send expeditions to discover the geographic distributions of plants (and animals) in the United States. The first of these was The Death Valley Expedition, including Frederick Vernon Coville, Frederick Funston, Clinton Hart Merriam, and others.
Research in plant geography has also been directed to understanding the patterns of adaptation of species to the environment. This is done chiefly by describing geographical patterns of trait/environment relationships. These patterns termed ecogeographical rules when applied to plants represent another area of phytogeography. Recently, a new field termed macroecology has developed, which focuses on broad-scale (in both time and space) patterns and phenomena in ecology. Macroecology focuses as much on other organisms as plants.
Branches of biology relevant to phytogeography
Phytogeography is part of a more general science known as biogeography. Phytogeographers are concerned with patterns and process in plant distribution. Most of the major questions and kinds of approaches taken to answer such questions are held in common between phyto- and zoogeographers.
Phytogeography is often divided into two main branches: ecological phytogeography and historical phytogeography. The former investigates the role of current day biotic and abiotic interactions in influencing plant distributions; the latter are concerned with historical reconstruction of the origin, dispersal, and extinction of taxa. Floristics is a study of the flora of some territory or area. Traditional phytogeography concerns itself largely with floristics and floristic classification, see floristic province.
- Alexander von Humboldt & Aimé Bonpland: Essay on the Geography of Plants. The University of Chicago Press, 2009. ISBN 978-0-226-36066-9 (cloth)
- Geobotanical prospecting
- Species distribution
- Association (ecology)
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- Death Valley Expedition (1891), Historic Expeditions, Smithsonian Museum of Natural History, 
- Brown, J.H. & Lomolino, M.V. 1998. Biogeography. 2nd edition. Chapter 1.
- Wallace, A. R. 1878. Tropical nature and other essays. Macmillan, London.
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- Frederic E. Clements (1920). "Plant Geography". Encyclopedia Americana.
- "Distribution of Plants". New International Encyclopedia. 1905.