Centred on the desert steppes of Central Asia and Mongolia, this floristic zone consists of 200 or more endemic genera and extends from the Caucasus to the Plateau of Tibet, with arid zone plants of the family Chenopodiaceae (goosefoot) and genera such as Salix (willow), Astragalus (milk vetch), and Picea (spruce) (Figure 1).
The Mediterranean region is the winter rainfall zone of the Holarctic kingdom (Figure 1). It is characterized by sclerophyllous plants mainly of the scrubland type known as maquis. It is difficult to define, however, because many of its characteristic plants (about 250 genera) are centred around but not confined to this region. The region extends entirely around the Mediterranean, from Portugal to Syria. Some classifications place the Canary Islands, which contain a subtropical rainforest biome, in this region, but Good categorizes these islands with the other eastern Atlantic island groups in a separate Macaronesian region, which contains about 30 endemic genera.
The Eurosiberian region extends from Iceland around most of Europe via Siberia to Kamchatka. Conifers of the family Pinaceae—Pinus (pine), Larix (larch), Picea, and Abies (fir)—grow in vast, monospecific stands and give way to temperate deciduous forest to the south, tundra to the north, and moorlands (which contain Ericaceae [heath family], Carex [sedge], and Sphagnum moss in suitable areas). The western part of the region is much richer in species than the eastern part: there are about 100 genera that are endemic to Europe, with only about 12 endemic to Siberia.
The vegetation to the east of the Bering Strait, in the North American region (Figure 1), closely resembles that to the west, in the Eurosiberian region, with slight variations. The conifer genera Tsuga (hemlock), Sequoia (redwood), and others replace their Eurosiberian counterparts, and there are nine endemic families of flowering plants. Good and others separate the eastern (Atlantic) and western (Pacific) halves of North America into distinct regions, with 100 genera endemic to the Atlantic region and 300 endemic to the Pacific, although these endemic taxa comprise only a small part of the total flora.
This kingdom extends from Africa, excluding strips along the northern and southern edges, through the Arabian peninsula, India, and Southeast Asia eastward into the Pacific (Figure 1). Plant families that extend over much of the region include the families Pandanaceae (screw pine) and Nepenthaceae (East Indian pitcher plant). The flora in this huge region, however, is not homogenous: 98 percent of species of Hawaiian flora are endemic, as are 70 percent of Fijian floral species and 60 percent of the floral species of New Caledonia. The divisions of the kingdom are disputed, but those most commonly recognized are the Malesian, Indoafrican, and Polynesian subkingdoms.
This subkingdom encompasses the islands of Southeast Asia and the Malay Peninsula, extending as far east as the mainland of New Guinea (Figure 3). Although it had sometimes been included with India in an Indo-Malayan region, the flora of what C.G.G.J. van Steenis (1950) called Malesia forms a tight-knit unity that can be subdivided into three divisions: a western area covering the Malay Peninsula, Sumatra, Borneo, and the Philippines; a southern area of Java and the Lesser Sundas; and an eastern area of Celebes, the Moluccas, and New Guinea. The region boasts approximately 400 endemic genera (20 percent of the total flora of the Earth), of which 130 genera are found in the western division, 15 in the southern division, and 150 in the eastern division. The biome types range from tropical rainforest to montane and cloud forest, with drier biome types in areas of the southern division. The rainforest biomes in the western part of the region are characterized by the dominance of the family Dipterocarpaceae, although the Guttiferae, Moraceae (mulberry), and Annonaceae (custard apple) families also are found throughout.
In the Indoafrican subkingdom (Figure 1), curiously little distinction is to be made between the flora of Africa (south of the Sahara) and the Indian subcontinent, Myanmar (Burma), and southern China. These areas are narrowly connected by a corridor running through the Arabian Peninsula and southern Iran. The flora of the island of Madagascar is the most divergent in the region and is often regarded as forming a separate region; the island has 12 endemic families and 350 endemic genera, although these form only about a quarter of the total. The flora of Sri Lanka has almost as much in common with Malesia as it does with India. Vegetation ranges from rainforest to semiarid steppe. The families Leguminoseae (legume) and Asteraceae (aster), often called Compositae, achieve their greatest diversity in the region, together with Combretaceae (Indian almond) and, in the arid south of Madagascar, Didiereaceae. Characteristic genera include the grasses Andropogon and Panicum and the giant baobab (Adansonia). In the montane (Afroalpine) zones Lobelia, Senecio, and Erica (heath) are characteristic. About 50 endemic genera define a desert zone extending from the Sahara to northwestern India; 500 are endemic to tropical Africa, 120 to India, and 300 to continental Southeast Asia, but the boundaries of these zones are poorly defined and the distributions of the endemics are only weakly coterminous.