BASICS OF PHYTOCOENOLOGY AND PLANT GEOGRAPHY - T. P. Larkina - 2017

SECTION 2. BASICS OF PLANT GEOGRAPHY

2.8. Floristic Kingdoms of the Globe

The Earth's vegetation cover is extremely diverse. Researchers have repeatedly attempted to categorize the existing Water/126.html">Diversity of the plant world into major taxonomic units, namely types. Through painstaking research conducted by many generations of botanists, data on the floras of various regions across the globe have gradually accumulated. Comparisons of these findings have revealed distinct floristic districts that differ in their floristic composition. It has proven possible to classify these floristic districts by taking into account the degree of these differences. Naturally, these differences must be evaluated based on whether the floras of any two districts differ merely in a few species, or whether they contain different genera or even families; it is also crucial to determine how many endemic taxa are present in the flora, what their rank is, and so on. Several such systems have been proposed: for instance, one of the earliest attempts to establish a terrestrial floristic system was made by the Danish botanist J. Schouw, who in 1823 identified 25 realms, subdividing some of them into provinces. As a criterion for constructing his floristic system, J. Schouw considered, in particular, the degree of endemism of various taxonomic ranks characteristic of specific territories. This criterion remains relevant to this day. A tremendous contribution to The Development of floristic regionalization was later made by A. Engler, L. Diels, R. Good, A. I. Tolmachev, and others. In the following Structure/133.html">Discussion, we will adhere to the regionalization system developed by A. L. Takhtajan (1978) (Fig. 29).

The highest unit of floristic regionalization is the kingdom, which exhibits the most pronounced distinctiveness. The rank of kingdom is assigned to regions characterized by the overall distinctiveness of their flora and the presence of high-ranking endemic taxa (families, subfamilies), combined with a very high number of generic and specific endemics. A total of six kingdoms are distinguished:

1. Holarctic;

2. Paleotropical;

3. Neotropical;

4. Australian;

5. Cape;

6. Antarctic.

The territories they occupy are shown in Figure 29.

Kingdoms are subdivided into subkingdoms and regions, which are characterized by high generic and specific endemism; furthermore, each region possesses a specific set of dominant families. In total, there are 34–35 regions, which are further subdivided into provinces. The lowest chorological unit is the district. Within this hierarchy of subordinate categories, the uniqueness of floras progressively decreases; the subordination of floristic districts is by no means related to the size of the territories they occupy, but rather depends on the degree of floristic uniqueness and the distinct historical development of their floras.

I. Holarctic Kingdom. In terms of area, this is the largest kingdom on the planet: it covers the greater part of the Northern Hemisphere's landmass—from the Arctic to the subtropics—encompassing all of Europe, extratropical Asia, extratropical North Africa, and almost all of North America and Greenland. Although there is still no consensus regarding the exact position of its southern boundary, its general outlines have been established. The Holarctic Kingdom encompasses a fairly well-defined and floristically relatively uniform territory characterized by numerous plant families and genera that either occur almost exclusively within this region or exhibit their centers of distribution here. Naturally, these are familiar and well-known families and genera, such as maples (Aceraceae), umbellifers or celery family (Umbelliferae, or Apiaceae), crucifers or cabbage family (Cruciferae, or Brassicaceae), pinks (Caryophyllaceae), birches (Betulaceae) and beeches (Fagaceae), roses (Rosaceae), primroses (Primulaceae), buttercups (Ranunculaceae), and others. The species-rich genus sedge (Carex) is also predominantly distributed here.

Such an extensive floristic kingdom encompasses territories with diverse climatic conditions, which naturally affects its floristic composition. Therefore, the floristic regions—numbering between 8 and 12 in the Holarctic Kingdom, depending on the researcher's perspective—generally correspond to different climatic zones while also featuring specific plant communities.

The Boreal Subkingdom has no analogues in terms of the area it covers. At the same time, it exhibits the highest level of endemism across all ranks, including generic and familial levels. Furthermore, within the Boreal Subkingdom, There is a significant number of clearly primary angiosperm families characterized by archaic structural features. Among gymnosperms, this includes ginkgo (Ginkgo biloba) (Fig. 18); among angiosperms, it includes polycarpous plants such as magnolias (Magnolia), the tulip tree (Liriodendron tulipifera) (Fig. 30), laurels (Laurus), and others. Some of these combine characteristics of both monocots and dicots.

Regions:

1. Circumboreal region.

2. East Asian region.

The Circumboreal and East Asian floristic regions are considered by some researchers as a single entity, whereas the majority divide this territory into A number of smaller regions. A. L. Takhtajan characterizes the Circumboreal region by low-ranking endemism. Endemic families are absent. Endemic genera are often monotypic. Examples include Redowskia (Yakutia), Pseudovisicaria (Caucasus), Tridactylina (Lake Baikal coast), and others. However, oligotypic and even polytypic lungworts—Pulmonaria (14 species)—and others are also found. Various forest formations—both coniferous and broad-leaved—are widespread throughout the Circumboreal region. The main forest-forming coniferous species belong to such genera as pine (Pinus), fir (Abies), larch (Larix), and spruce (Picea); in the Western Hemisphere, these are joined by species of hemlock (Tsuga) and arborvitae (Thuja). Broad-leaved forests are formed by various species of oak (Quercus), beech (Fagus), maple (Acer), hornbeam (Carpinus), birch (Betula), poplar (Populus), willow (Salix), ash (Fraxinus), walnut (Juglans), elm (Ulmus), and a number of less prominent forest species, such as hackberry (Celtis), dogwood (Cornus), hawthorn (Crataegus), rowan (Sorbus), viburnum (Viburnum), buckthorn (Rhamnus), and others (Fig. 31).

In addition to the widespread forest formations, vast areas are occupied by various herbaceous vegetation formations. Bogs predominate in high latitudes, while meadows are more common further south.

Partly in Siberia, but especially extensively in the European part of our country, the forest zone transforms into a forest-steppe zone under METABOLISM/18.html">The Influence of overall soil and climatic conditions: meadows transition into steppes (Fig. 32). The steppes were plowed up in the mid-20th century due to the rapid development of agriculture.

Moving south and southeast within the Boreal Subkingdom, one can easily observe how the species-poor arctic and taiga flora gradually transforms into the rich, subtropical flora of Southern China, which lies within the East Asian province.

The subtropical forests of Southern China lack clearly dominant tree species, unlike our taiga, for instance. Mixed forests prevail here, structurally and physiognomically reminiscent of tropical forests. The impression of similarity to Old World tropical forests is reinforced by the warm and humid climate, an almost continuously active vegetative cover, and the presence of numerous lianas and epiphytes. The only elements missing are species of the screw pine family (Pandanaceae) and pitcher plant family (Nepenthaceae), which are characteristic of tropical forests; typical Components of the Paleotropics such as cherry laurel (Laurocerasus), cycads (Cycas), and palms (genera Phoenix, Livistona, Areca, etc.) are also poorly represented.

As one moves from the subtropics of Southeast Asia to higher latitudes in East Asia, the vegetation cover changes significantly. Starting at approximately 45° north latitude (slightly higher in Japan), a snow cover appears, serving as an insurmountable barrier for most evergreen subtropical species. The kaleidoscopic diversity of forest-forming trees and the shrub understory diminishes. Winters at these latitudes are longer and harsher; consequently, deciduous species predominate among broad-leaved trees, their trunks are less frequently draped with epiphytes, and they are entwined with less robust and less structurally and taxonomically diverse lianas. The impoverishment of species composition and life forms occurs relatively gradually, driven entirely by climatic shifts. Under the milder marine climate of Southern and Central Japan and Korea (the Sino-Japanese province), colorful and species-rich subtropical forests can still be found. There are numerous broad-leaved deciduous species: beech (Fagus sieboldii), oaks (Quercus), maples (Acer), ashes (Fraxinus), lindias/limes (Tilia), hazelnuts (Corylus), and others. An enormous number of endemic species and genera, and even one family (Glaucidiaceae), are observed within this province. Such a significant scale of endemism is evidence of this province's even greater floristic richness in the past.

Moving northward and northeastward within the region, the appearance of the vegetation cover changes. The mixed forests of the Manchurian province consist entirely of deciduous angiosperm species. In the mountains of Manchuria and the Amur Region, conifers form continuous forests, much like in the North Chinese province. Depending on local soil and climatic conditions, one of the primary forest-forming species dominates these woods.

Following north from the Yablonoi Range, well within the Circumboreal region, one enters a novel and distinctive landscape: the Siberian taiga (Fig. 33). These are the northernmost forests, exquisitely adapted to the harsh conditions of a long and cold winter. The Siberian taiga stretches far to the west into Western Siberia and crosses the Ural Mountains.

In the north of Eastern and Western Europe, coniferous forests—the taiga—are formed by new tree species. In a distinctly "Europeanized" form, the taiga reaches the shores of the Atlantic Ocean. Coniferous forests are heavily impoverished in terms of the number of tree, shrub understory, and herbaceous cover species, as well as life forms. Vast expanses are occupied by light deciduous larch forests, where the herbaceous ground cover and shrub understory develop most luxuriantly.

A special type of Siberian taiga is formed by fir and spruce forests. The densely closed canopies of evergreen species create a dark, thick canopy. The shrub understory and herbaceous cover are extremely sparse. Mosses are well represented here, while ferns and a few shade-tolerant herbaceous perennials—such as wood sorrel (Oxalis acetosella), chickweed wintergreen (Trientalis europaea), and one-flower wintergreen (Maianthemum bifolium)—along with dwarf shrubs like bilberry (Vaccinium myrtillis), are less common. A unique type of taiga, known as *kedrachi*, is formed by the Siberian pine (Pinus sibirica) across the mountainous expanses of Siberia. High in the mountains, a special variety of pine (P. pumila) forms nearly impenetrable thickets (dwarf cedar). In the taiga, typically on sandy soils, a distinct forest type known as pine forest (*bory*) is widespread, formed by Scots pine (P. sylvestris L.). Its understory Supports a sparse and monotonous herbaceous vegetation, dominated by Lichens, primarily Cladonia rangiferina and Cetraria islandica (Fig. 11).

Vast forest expanses, spanning tens of thousands of square kilometers, are formed by just five main tree species: Siberian larch (Larix sibirica), Siberian spruce (Picea obovata), Siberian fir (Abies sibirica), Siberian pine (Pinus sibirica), and Scots pine (Pinus sylvestris L.).

Broad-leaved deciduous species, so characteristic of the Manchurian and, especially, the Sino-Japanese provinces, are entirely absent here. Small, isolated islands of small-leaved lime (Tilia parvifolia) have survived only in parts of Siberia, such as the Kuznetsk Alatau and the Altai Mountains.

Across the vast expanse of the Siberian taiga, large-leaved deciduous species accompany the dominant conifers. Only in burned areas do alder, birch, and aspen form short-lived pure stands.

Significant areas of the Siberian taiga are occupied by bogs, predominantly raised sphagnum bogs. Here, typical bog species are abundant: cranberry (Oxycoccus quadripetala), cloudberry (Rubus chamaemorus), bog blueberry (Cranberry uliginosum), marsh Labrador tea (Ledum palustris), and others.

To the west and southwest of the Ural Mountains, the climate changes noticeably: winters are milder and shorter, and the warming Influence of the Atlantic Ocean is increasingly felt. The dominant tree species of the Siberian taiga—Siberian pine, followed by Siberian spruce, larch, and fir—gradually diminish and wedge out. Here, they are replaced by European conifers: Norway spruce (Picea excelsa), European larch (Larix decidua), and silver fir (Abies alba). As in the east of the continent, within the Manchurian and Sino-Japanese provinces of the East Asian Floristic Region, broad-leaved tree species appear. Both forest and herbaceous vegetation become increasingly diverse and variegated. In the middle latitudes of the European part of the former USSR, and especially further west and southwest, broad-leaved forests (oak groves) emerge. The main forest-forming species include English oak (Quercus robur, Q. petrea, etc.), European beech (Fagus sylvatica), maples (Acer platanoides, A. pseudoplatanus), limes (Tilia cordata, T. cordifolia, etc.), European ash (Fraxinus excelsior), and others. Already in the East European province (the Ukrainian Carpathians, Poland), continuous forest massifs are formed by beech. Like Siberia, Europe is part of the Circumboreal Floristic Region. The immense expanses of Siberia (the Middle and West Siberian provinces) are characterized by a fairly uniform landscape and vegetation cover, which is explained by a relatively smooth, albeit harsh, continental climate, as well as specific relief and soils. Europe presents the exact opposite picture: proximity to oceans and warm seas, a highly indented coastline, complex geomorphology, diverse soil types, and contrasting climatic conditions have all combined to drive the development of an extraordinarily varied vegetation cover. Indeed, Europe boasts not only diverse but even contrasting vegetation types: coniferous and mixed broad-leaved forests, forb-grass, grass, and wormwood-grass steppes, mountain and floodplain meadows, bogs, and semideserts.

It is easy to imagine that the flora of Europe is characterized by both species richness and A wide variety of life forms. The originality of this flora is evidenced by a high rate of endemism, reaching 15–18% of the total number of species. Naturally, such a high percentage of endemism is found in the continent's mountain regions, such as the Eastern Alps. The rank of endemism is relatively low, primarily at the species level, with very few endemic genera.

Botanical-geographical zonation of Europe within the broad framework of the Circumboreal Floristic Region is quite challenging. In any case, the number and rank of distinguished chorions, especially their boundaries, remain a subject of discussion. For instance, the expediency of designating the Arctic as a distinct floristic province is currently debated. In this regard, Soviet botanist V. Vasilyev reasonably argues that the tundra zone of the corresponding meridional segment of the forest zone is merely an impoverished derivative of it. Europe is divided into several provinces: North European, East European, Central European, Atlantic European, and Balkan (Illyrian). To the southeast, these are adjoined by the Euxine (primarily Colchic-type floras of the Western Caucasus coast, European Turkey, and southern Bulgaria) and Caucasian provinces. Both share much in common in their vegetation structure. Deciduous forest formations (oak, beech, hornbeam, chestnut) dominate in both regions, and their forest-forming species vary in taxonomic composition. However, they share common lianas, such as ivy (Hedera colchica and H. helix) and smilax (Smilax excelsa), as well as two shared endemic genera—Agasilis and Sredinskya—and A large number of common species. Evergreen shrubs are widely represented, including pontic rhododendron (Rhododendron ponticum), Colchic butcher's-broom (Ruscus colchicum), and cherry laurel (Laurocerasus officinalis). The BOUNDARIES OF THE Euxine and Caucasian provinces are controversial due to complex florogenetic links with provinces not only of the Circumboreal Region, but also of the Irano-Turanian (Armeno-Iranian province) and Mediterranean (especially the Crimean-Novorossiysk) regions. Species and even isolated vegetation patches characteristic of these provinces deeply interpenetrate one another. When mapping the flora of these provinces, it becomes clear that in many areas they explicitly overlap.

In the Western Hemisphere, the Boreal subkingdom of the Holarctic is represented by two floristic regions: the Atlantic-North American region and the Rocky Mountain region. Within these two regions, a total of five provinces are distinguished.

3. Atlantic-North American Region. This vast region extends from the Atlantic coast of North America to the Great Plains, and latitudinally from the Gulf of Mexico coast to the Lake District (southern regions of Canada). In the Atlantic states, the natural vegetation is represented by forest formations. In their appearance and dominant tree composition, they remarkably resemble the forests of the southeastern provinces of the East Asian region (China, Japan). Broad-leaved deciduous species clearly dominate here, while conifers and evergreen hardwoods are relatively rare. Further north, the main massifs of Canadian forests are formed by fir (Abies amabilis, A. concolor) (dark coniferous forests) or larch (Larix americana). Spruce (Picea alba) extends furthest to the north. In its overall appearance, including the similarity of its dominant tree species, the Canadian taiga is closely related to the Siberian taiga. Among small-leaved species, the Canadian taiga features Representatives of the same genera: paper birch (Betula papyrifera, close to the European B. pendula) and poplars, which replace the Eurasian aspen (Populus tremula).

As one moves toward the southern foothills of the Appalachian Mountains and the Florida Peninsula, evergreen hardwoods become increasingly common in the mixed forests. In the Atlantic Coastal Plain province, which encompasses almost the entire Florida Peninsula, subtropical species such as palms, laurels, magnolias, bay trees (Persea), pawpaws (Asimina), and others are frequently encountered. The southern part of Florida features mangrove forests and various elements of the tropical Caribbean and Mexican flora, such as species of the genera Vernona, Cyperus, and Sabal. The latter confirms the high rank and scale of endemism: one family and about a hundred endemic or near-endemic genera, most of which are monotypic. When comparing and analyzing the floras of the world, scientists noted a paradoxical fact as early as the beginning of the last century: the flora of Southeast Asia is genetically closer not to neighboring Europe, but to the overseas flora of the Atlantic states of North America. This floristic affinity is expressed not only in shared genera but also in closely related vicariant (corresponding) species. In the mid-19th century, American botanist Asa Gray explained these facts by species exchange between Asia and North America, which naturally presupposes: 1) contact in the geological past and 2) a milder climate in the north of these continents.

The Atlantic-North American Region is subdivided into the following provinces: the Appalachian, the Atlantic Coastal Plain, and the North American Prairie. The flora of the latter two provinces is recognized as young, representing a derivative of the older flora of the Appalachian province. Distinctive prairie grasses such as Andropogon gerardii, A. scoparius, Sorghastrum nutans, and Spartina pectinata are most likely immigrants from the eastern forests.

4. Rocky Mountain Region. This region stretches along the Pacific coast of North America and is represented by mountain systems from Alaska to New Mexico (Western Canada and the USA). Coniferous forest formations dominate here. In the richness of their forest-forming tree species, these forests have no analogs. Alongside species corresponding to the conifers of East Asia, local (autochthonous) species have evolved here, including western hemlock (Tsuga heterophylla and T. mertensiana), western red cedar (Thuja plicata), Douglas fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), and lodgepole pine (P. contorta). Broad-leaved deciduous species also occur within these forests.

In the southern part of the region—from the Mouth of the Oregon River to the Gulf of California and inland—lies an area distinguished by a milder climate. Here, about 30 conifer species are concentrated, among them giants of the plant world such as the giant sequoia (Sequoiadendron giganteum), coast redwood (Sequoia sempervirens), and others (Fig. 16). The understory contains many small-leaved evergreen shrubs. A unique character is imparted to the flora by typical New World angiosperm species, such as arborescent lilies (genus Yucca), cacti, and palms (Pritchardia). Endemism among seed plants, although rich, is predominantly at the species level. Families richest in endemic genera and species include Brassicaceae, Saxifragaceae, Rosaceae, Asteraceae, and others. Only a single endemic family is represented in the flora here: Gyrothyraceae (liverworts). The region is divided into two provinces: the Sitkan-Oregon province and the Rocky Mountain province.

Paleo-Mediterranean Subkingdom. Around the Mediterranean Sea, stretching far to the west into Macaronesia, and eastward through Western and Central Asia to Mongolia and the Gobi Desert, lies a distinct subtropical flora known broadly as the Mediterranean flora.

The northern boundary of this flora is formed by the mighty mountain chains of the Caucasus, the Balkans, the Alps, and the Pyrenees. Scientists' opinions differ regarding the taxonomic rank of this flora and its boundaries. It was first described by A. Engler (1881) at the rank of a botanical-geographical region: Ancient Mediterranean (Mediterranis).

Compared to his predecessors, A. de Candolle and E. Boissier, he significantly advanced the boundaries of the Mediterranean eastward. Subsequently, the boundaries of the Mediterranean flora expanded considerably, and its taxonomic rank was elevated to a subkingdom (A. L. Takhtajan) and even to a distinct floristic kingdom (W. Schäfer).

The Mediterranean flora is fundamentally adventive and migratory. It formed across the vast expanses of the drying Tethys Sea floor, where two genetically dissimilar floras converged: from the north and northeast, the boreal flora (the Ginkgo flora according to M. G. Popov), and from the south, the tropical, primarily African flora (the Welwitschia flora). The junction (collision) of these two floras is evidenced by many Mediterranean species—most often xerophytes or geophytes in their ecology—that have relatives in the flora of South Africa. Closely related bonds have been traced across an entire series of flowering genera. We cite only a few of them: flax (Linum), carnation (Dianthus), bindweed (Convolvulus), sage (Salvia), gladiolus (Gladiolus), and iris (Iris).

Within the Mediterranean Subkingdom, the following regions are distinguished:

5. Macaronesian.

6. Mediterranean.

7. Saharo-Arabian.

8. Irano-Turanian.

Two of them—the Mediterranean and the Irano-Turanian—are of particular interest because: 1) vast expanses of Russia are part of these regions; 2) their flora has significantly influenced the development of extratropical floras in the Northern Hemisphere; 3) the territories of these regions harbor the centers of origin for many agricultural species.

Madrean (Sonoran) subkingdom:

9. Madrean (Sonoran) region.

It extends from southwestern Oregon through California to the northern part of Baja California, and includes the hot deserts from Southern California to Arizona, New Mexico, and Texas, stretching further south to the Mexican Plateau, most of Nevada and Utah, and isolated parts of adjacent states.

When subdividing floristic regions into provinces, primary consideration is given to circumstances associated with the historical development of floras, particularly the consequences of the Ice Age.

II. Paleotropical kingdom. In terms of area covered, this kingdom ranks second, but in the number of species, it is the richest among all floristic kingdoms. It encompasses the tropics and subtropics of the Old World, that is, most of Africa, Southwest Asia, India, Southeast Asia, and the Pacific islands. As for New Zealand, some researchers classify it within the paleotropical kingdom, while others assign it to the Australian or Antarctic kingdoms.

South of Holarctis, between the two tropics (extending slightly north of the Tropic of Cancer and south of the Tropic of Capricorn), lie two floristic kingdoms: in the Western Hemisphere—the Neotropical (Neotropis), and in the Eastern—the Paleotropical (Paleotropis). In terms of territory, the Paleotropical kingdom ranks second after the Holarctic. It occupies vast expanses in Africa (south of the Sahara Desert, with the exception of the small southwestern tip of the continent—the Cape floristic kingdom, see below), the southwestern part of the Arabian Peninsula, New Guinea, New Zealand, the northern and northeastern coasts of Australia, and the tropical islands of the Pacific Ocean (the Philippines, the Malay Archipelago, as well as the Fiji, Samoa, and Sandwich Islands, etc.). Despite the extreme fragmentation and dispersion of this kingdom, paleobotanical data indicate The Unity of its flora, which is the most ancient and conservative.

Numerous species of the families Pandanaceae, Nepenthaceae, and Dipterocarpaceae are widespread in the Old World tropics. A whole series of distinct genera characterizes this flora. For instance, among palms, only here do we find the famous date palm (Phoenix), as well as Caryota, Corypha, Livistona, Calamus, and others.

The Stability of the climate—warm year-round (20–27 °C) and humid (up to 14,000 mm of precipitation per year)—ensures the relative stability of biogeocenoses. Ongoing changes in The structure of the plant cover here and there are increasingly driven primarily by anthropogenic factors: forest burning, ruthless logging of high-value tree species, etc.

The Paleotropical kingdom is divided into five subkingdoms comprising 12 regions. Based on the characteristics of their floras, the paleotropical kingdom is split into the Indo-African (western) and Malesian (eastern) parts. This subdivision is due to differences in the historical development of their floras.

Indo-African floristic region (the western part of the paleotropical kingdom). Regionally, this area unites tropical Africa, Southwestern Arabia, Madagascar, India, and the Indian Ocean islands up to the island of Ceylon, i.e., up to the 80th meridian east longitude. The fundamental difference between this region and the next is defined either by the Location of genera found nowhere else, or by the concentration of the absolute majority of species belonging to these genera. These primarily include species of palm genera such as Borassus, Phoenix, Raphia, Elaeis, as well as the coco de mer (Lodoicea seychellarum—an endemic of the Seychelles); from the Sterculiaceae family, the cola tree (Cola); from the Santalaceae, Santalum; and from the bamboo subfamily, Bambusa. Lush mangrove forests thrive along the ocean coast. This is a unique plant formation. Mangroves have evolved special adaptations ensuring their survival under tidal conditions: viviparity and stilt roots. The dominant species here belong to the genera Rhizophora (family Rhizophoraceae), Avicennia (family Verbenaceae), and others.

A particular highlight of the paleotropics is the savanna. These are areas of tall grasses (up to 3 m in height), punctuated by branching trees up to 20 m tall—the famous baobab (Adansonia digitata), thorny umbrella-crowned acacias (Acacia spirocarpa, A. senegal, A. graffe), and many other species. The tall grasslands are dominated by elephant grass (Pennisetum species), millet species (genus Panicum), and alang-alang grass (Imperata cylindrica).

The South African Kalahari and Namib deserts are also characterized by a unique floral composition and specific plant formations. Drought-resistant plants predominate here: numerous succulents, especially of the genera Euphorbia, Aloe, and Mesembryanthemum. A particular marvel of these hottest deserts on Earth is the paleoendemic Welwitschia mirabilis (Fig. 34).

The Indo-African region is an ancient center of agricultural culture. A vast assortment of crops is cultivated here. Among the cereals are rice, wheat, corn, barley, and sorghum; many vegetable and fruit crops are grown, such as potatoes, bananas, citrus fruits, cucurbits, and date palms, alongside other food and industrial crops: cotton, tobacco, jute, sugarcane, and the cacao tree.

The Malesian region (the eastern part of the paleotropical kingdom) occupies a territory noticeably smaller than the Indo-African one. It encompasses Indochina, Ceylon, and a number of other Pacific islands, the most important being the Sunda, Philippine, and New Zealand islands. One of the Characteristic Features of this region is its high species richness. Palms are represented by a great variety of species. Among them, rattans (Calamus), betel nut palms (Areca catechu), and others are frequently encountered in monsoon forests. Other systematic groups that impart uniqueness to the flora include the breadfruit tree (Artocarpus), camphor laurel (Camphora), and black pepper (Piper nigrum). It is also here (on the island of Sumatra) that a peculiar parasite is found—Rafflesia arnoldii (Fig. 35).

The plant body of this Organism is extremely reduced. Only haustoria, which penetrate the host's Tissues, are well-developed. However, the flower reaches a record size—1 m in diameter.

The vegetation cover is physiognomically relatively uniform. Rain forests and monsoon forests dominate. A large list comprises the crops cultivated here. Most of them have been introduced from other floristic regions (cereals, sugarcane, cotton, pineapple, tobacco, cinchona, etc.). Sago palms (genus Metroxylon), black pepper (Piper nigrum), nutmeg (Myristica fragrans), the clove tree (Syzygium aromaticum), and indigo (Indigofera) are of local (autochthonous) origin. Indigo is successfully cultivated in the south of Russia, in Crimea (Yalta,

Nikitsky Botanical Gardens) as a valuable dye plant.

Of all plant genera living in the tropics, approximately 47% are found in the paleotropical kingdom, 40% in the neotropical, and only 13% are common to both floristic kingdoms; these are the so-called pantropical genera. Pantropical species, however, are extremely few. There are also many families whose representatives occur in either one or the other floristic kingdom, or at least exhibit centers of distribution in one of them. We will mention only a few of such taxa, as most of them are scarcely known to non-specialists. Predominantly represented in the paleotropical kingdom are Nepenthaceae, Pandanaceae, Myristicaceae, Asclepiadaceae, Dipterocarpaceae, the stem-succulent group of the genus Euphorbia, many Moraceae—especially the genus Ficus—and genera from the family Liliaceae, such as Aloe, Sansevieria, and Dracaena.

African subkingdom:

10. Guineo-Congolian region.

11. Sudano-Zambezian region.

12. Karoo-Namib region.

13. Region of Saint Helena and Ascension Islands.

Madagascan subkingdom:

14. Madagascar region.

Indo-Malayan subkingdom:

15. Indian region.

16. Indochinese region.

17. Malayan region.

18. Fijian region.

Polynesian subkingdom:

19. Polynesian region.

20. Hawaiian region.

New Caledonian subkingdom:

21. New Caledonian region.

III. The Neotropical realm is located in the New World, encompassing the territory south of the Baja California–Florida line, in other words, the entirety of Central America and almost all of South America. Its most characteristic families include Bromeliaceae, Cactaceae, Tropaeolaceae, Cannaceae, Melastomataceae, and others. Representative genera include Yucca, Agave, and Fuchsia. The Neotropical realm is exceptionally rich in endemics. The Neotropical (Neotropis) realm is distributed across Middle and South America (excluding the southernmost part of the continent, Chile, and Patagonia), Southern Florida, the Antilles, and the Galapagos Islands.

Floristically, this is the most ancient, distinct, and species-rich realm (comprising 40,000 species according to R. Good). Many families and genera rich in diverse species are found exclusively within the Neotropics, and most likely originated here. Among the major systematic groups unique to the New World tropics is the large cactus family (Cactaceae), which numbers about 1,800 species. In the Old World tropics, these are ecologically replaced by succulent euphorbs and aloes. A distinctive flair is imparted to the tropical forests by a wide variety of epiphytes, some belonging to the Bromeliaceae and others to the Orchidaceae. Bromeliads are characteristic exclusively of the humid tropical forests of the Americas; all of them are epiphytic or terrestrial herbs. The orchid family is particularly well-represented here, with certain genera occurring only in tropical America (such as Oncidium and Stanhopea). Families restricted solely to the New World also include Cannaceae, Julianiaceae, Tropaeolaceae, and Marcgraviaceae. The family Cannaceae is monotypic, with the genus Canna represented by highly ornamental species. These are giant herbs with large, brightly colored red or orange flowers, which have been widely introduced in the Eastern Hemisphere.

V. Alekhin characterizes the floristic wealth of the Neotropics as follows: Brazil — 40,000 species, Mexico — 7,040, Venezuela — 6,800, Cuba — 7,000, Chile — 5,500, Paraguay — 4,200.

Within the Neotropics lies the geographic range of the Cyclanthaceae family, which are closely related to palms, as well as the ranges of several palm genera, notably coconut (Cocos). It is also home to 40 species of Cinchona (the quinine tree) and other genera of The Madder family (Rubiaceae).

The Neotropical realm is differentiated into five floristic regions:

22. Caribbean region.

23. Guiana Highlands region.

24. Amazonian region.

25. Brazilian region.

26. Andean region.

IV. The Cape realm. Although the Cape floristic realm is the smallest in terms of area (occupying the southernmost tip of the African continent), it encompasses over 6,000 species of flowering plants and is characterized by exceptional morphological diversity and an Abundance of endemic taxa. The Cape flora differs strikingly from the African flora of the Paleotropical realm, yet certain families (particularly Proteaceae and Restionaceae) indicate its affinity with the Australian and Antarctic floristic realms. Some genera of the family Proteaceae are native exclusively to this realm, for instance, Protea, Leucadendron, and others. Furthermore, numerous genera from other families are represented by a multitude of species found nowhere else, such as the genus Mesembryanthemum (leaf succulents) and other genera of Aizoaceae, the genus Pelargonium (nearly 250 species) from Geraniaceae, the genus Clivia from Amaryllidaceae, and the genera Haworthia and Gasteria (leaf succulents) from Liliaceae. Many of these plants are commonly cultivated as indoor ornamentals. In addition, the Cape flora is extraordinarily rich in representatives of the heath family (Ericaceae). The genus Erica even exhibits a secondary center of diversity in the Cape floristic realm, with no less than 500–600 of its species occurring in this small territory.

27. Cape region.

V. The Australian realm. This realm comprises Australia and Tasmania. Having separated from other continents at a very early date, Australia and Tasmania evolved in isolation for a long time. As a result, the Australian realm has emerged as the most distinctive and unique among all floristic realms, holding a special status. Out of approximately 10,000 native plant species there, over 8,600 are endemic; the vast majority of genera are likewise endemic. Among the most characteristic are the genus Eucalyptus, which includes about 500 species; the genus Melaleuca from the family Myrtaceae, containing 100 species; the remarkable grass trees of the genus Xanthorrhoea, related to the Liliaceae; and the family Casuarinaceae. More than half of the species of the very large genus Acacia (which contains 700–800 morphologically highly diverse species) are also found exclusively in the Australian floristic realm. The family Epacridaceae, closely related to Ericaceae and numbering 400 species, effectively ecological replaces the heath family in the Australian realm. The Australian realm is subdivided into:

28. The North-East Australian Province.

29. The South-West Australian Province.

30. The Central Australian, or Eremaean, Province.

VI. The Holantarctic Kingdom. In addition to Antarctica, which is inhabited by only a few plant species, the Antarctic kingdom includes the islands of the Southern Ocean (Falklands, Kerguelen, etc.) and the southernmost part of South America (Western Patagonia, Tierra del Fuego) along with the arc of islands lying to the south of it. Many researchers also include New Zealand, or at least its South Island, in this floristic kingdom. Various families comprise 13 specific genera of the Antarctic kingdom, for example, Azorella (from the Apiaceae family), which forms unusually dense cushions, Gunnera (from the Gunneraceae family), some species of which have very large leaves, and the southern beech — Nothofagus (from the Fagaceae family). The Holantarctic Kingdom includes:

31. The Juan Fernández Province.

32. The Chilean-Patagonian Province.

33. The Subantarctic Islands Province.

34. The New Zealand Province.

When considering the position and size of the six aforementioned floristic kingdoms, one immediately notices that their territories become progressively smaller and more fragmented toward the south. The entire extratropical landmass of the Northern Hemisphere is occupied by a single floristic kingdom — the Holarctic — whereas the tropical and subtropical regions are shared by two, and the areas lying even further south by as many as Three kingdoms. This reflects The history of the land and the concurrent history of flora development. It is known that continental breakup began in the southern regions and subsequently intensified further north. At the same time, shared

floral elements across different kingdoms indicate that the plant life of some floristic kingdoms was not isolated from that of others.

2.9. Botanical and Geographical Zoning of Perm Krai

In Perm Krai, S. A. Ovesnov (2007) identifies 6 botanical and geographical regions (Fig. 36):

1. The Region of Middle Taiga Fir and Spruce Forests.

Middle taiga forests are characterized by a simple stand structure; the shrub layer is either entirely absent or very weakly developed, while the herb-dwarf shrub and moss layers are quite well developed. Broad-leaved forest (nemoral) elements are weakly represented. Two subregions can be quite clearly distinguished within this area:

a — dominated by North European pine and spruce forests,

b — dominated by Kama-Pechora-West Ural fir and spruce forests.

Overall, forested land accounts for more than 85% of the region.

2. The Region of South Taiga Fir and Spruce Forests:

Compared to middle taiga forests, south-taiga forests are characterized by a more complex structure, the dominance of boreal species in the tree stand and understory with the participation of nemoral species, the coexistence of boreal and nemoral species in the herb-dwarf shrub layer, a noticeable increase in The Role of herbs compared to dwarf shrubs, and the predominance of herbaceous forest types, as well as a shallow, discontinuous moss cover. This region belongs to the Kama-Pechora-West Ural subprovince of the Ural-West Siberian taiga province. It comprises two subregions:

a — dominated by agricultural lands (accounting for 25–50% of the subregion's territory, with forested lands covering 35–55%),

b — dominated by aspen and birch forests replacing southern taiga dark-conifer forests (agricultural lands account for 6–10%, and forested lands for 75–85%).

3. The Region of Broad-Leaved, Spruce, and Fir Forests. The forests of this region are characterized by the most complex structure: the coexistence of boreal and nemoral species in the tree stand, with the latter predominating in the understory and herb layer. The tree canopy consists of 2–3 sub-canopies, with broad-leaved species (small-leaved lime, less frequently wych elm, Norway maple, European white elm, and pedunculate oak) forming The basis of the 2nd and 3rd sub-canopies. The shrub layer is typically well developed. The herb cover is generally continuous, tall, and consists of 3–4 sub-canopies; ferns and tall herbs make up a significant proportion, while dwarf shrubs are practically absent. The moss cover is poorly developed and usually tends to occur in patches near dark-conifer clumps. From north to south, there is a Transition Between Two subzonal community groups — complex nemoral-herbaceous fir-spruce forests and proper broad-leaved-spruce-fir nemoral-herbaceous forests. The boundary between them is gradual and blurred by human economic activity; it runs along the line of Chastye — Osa — Uinskoe. Forested land here accounts for 30–45%, while agricultural land covers 35–55% of the total area.

4. The Region of the Insular Kungur Forest-Steppe is located within the belt of broad-leaved, spruce, and fir forests. Small patches of forest have survived only on the hills. These are primarily birch and aspen forests with the participation of lime and elm, nemoral-herbaceous forests, and pine forests mixed with Siberian larch, often with lime in the understory, as well as foothill grassy forests. The high bedrock riverbanks feature limestone outcrops known as "kameny" (rocks), alternating with turf-covered areas supporting meadow and forest vegetation. Steppe patches occur on both leveled watersheds and slopes. The region is heavily altered by human activity, with agricultural lands occupying 40–55%, whereas forested lands account for only 10–20%.

5. The Region of Middle and South Taiga Foothill Fir-Spruce and Spruce-Fir Forests. Middle taiga foothill forests differ from lowland ones by a greater admixture of fir and Siberian pine (cedar), the predominance of herbs over dwarf shrubs, and the widespread occurrence of herbaceous, especially fern-dominated, forest types. South taiga foothill forests are characterized by a greater participation of nemoral species and a wider variety of herbaceous forest types compared to the lowlands. Here, the presence of Siberian species is higher, and an admixture of larch and cedar is characteristic. Overall, this is a forested region (forested lands occupy 85–95% of the total area), but the forests, as across the Krai as a whole, have undergone intensive logging, meaning significant areas are covered by secondary birch and mixed forests. The highest mountains, located in the areas of Mt. Oslyanka (1119 m), Mt. Middle Baseg (994 m), Mt. Zolotoi Kamen (892 m), and several others, exhibit a distinct altitudinal zonation with vegetation characteristic of the mountain forests of the north and middle taiga zones. Meadows (predominantly secondary) are few, accounting for no more than 0.5–1.5% of the area. Despite higher precipitation here compared to the middle and south taiga forest regions, waterlogging is less pronounced (peat bogs occupy 1–2% of the total area). Waterlogging is hindered by the rugged topography, as well as the abundance of rivers and streams. As in the Kungur forest-steppe, limestone outcrops ("kameny") are widespread, found along steep riverbanks as well as in large ravines. Agriculture is poorly developed; the proportion of land used for agricultural production does not exceed 2.5%.

6. The Region of North and Middle Taiga Cedar-Spruce Mountain Forests. This region concentrates the highest mountains of Perm Krai, a number of which exceed 1000 m above sea level. Consequently, altitudinal zonation is well expressed here. The features of mountain forests include sparse tree canopies, a constant natural admixture of downy birch, and the presence of cedar. The understory is sparse and species-poor. Hypoarctic and boreal species predominate in the herb-dwarf shrub layer, arcto-alpine plants are present, dwarf shrubs are characteristically dominant, and species diversity is low. The moss cover is thick, locally interrupted by patches of fruticose lichens. The high peaks of the Ural Mountains harbor islands of mountain tundras with an increased presence of arcto-alpine species combined with crustose and foliose lichen communities, as well as spruce and birch elfin woodlands alternating with tall-herb and short-herb subalpine meadows.