The Arcto-Tertiary Geoflora is a hypothesized flora

Flora

Flora is the plant life occurring in a particular region or time, generally the naturally occurring or indigenous—native plant life. The corresponding term for animals is fauna.-Etymology:...

l assemblage that once covered the Northern Hemisphere

Northern Hemisphere

The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

, from roughly the late Mesozoic

Mesozoic

The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

 to mid Cenozoic Eras.

Origins

First proposed by the paleobotanists

Paleobotany

Paleobotany, also spelled as palaeobotany , is the branch of paleontology or paleobiology dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments , and both the evolutionary history of plants, with a...

 J.S. Gardner and C. Ettinghausen in 1879, the concept was intended to answer questions about the disjunct distribution

Disjunct distribution

In biology, a taxon with a disjunct distribution is one that has two or more groups that are related but widely separated from each other geographically...

 of identical or closely related plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

 species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

: for instance, magnolia

Magnolia

Magnolia is a large genus of about 210 flowering plant species in the subfamily Magnolioideae of the family Magnoliaceae. It is named after French botanist Pierre Magnol....

 and tulip tree

Liriodendron

Liriodendron is a genus of two species of characteristically large deciduous trees in the magnolia family .These trees are widely known by the common name tulip tree or tuliptree for their large flowers superficially resembling tulips, but are closely related to magnolias rather than lilies, the...

s are native to both the Southeast United States and southern China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 and Indochina

Indochina

The Indochinese peninsula, is a region in Southeast Asia. It lies roughly southwest of China, and east of India. The name has its origins in the French, Indochine, as a combination of the names of "China" and "India", and was adopted when French colonizers in Vietnam began expanding their territory...

.,

As envisioned, the ATG had a wide distribution when the global climate was much warmer than it is currently, a situation strengthened by the closer position of some of the continents in late Mesozoic to early Cenozic times., With the onset of global cooling and the Ice Age

Ice age

An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

s, the ranges of these tropical to subtropical species were left in isolated pockets of warmer climates.

The southern, more tropical equivalent of the ATG was the Neotropical Tertiary Geoflora.