Plant Endemism and Biodiversity Conservation in the Alashan–Ordos Dryland of Inner Mongolia

Abstract

The East Alashan–Ordos Dryland of Inner Mongolia, China is the core area of the South Mongolian region, and one of the eight biodiversity centers in China. The plant biodiversity in the East Alashan–Ordos Dryland is diverse and unique, but its distribution and characteristics are yet to be well understood. Our results indicate that there are 5 endemic genera (Tetraena, Potaninia, Tugarinovia, Stilpnolepis, and Pugionium) and 2 Central Asian desert endemic genera (Ammopiptanthus and Elachanthemum) in this region. These 7 local and semi-local endemic genera are all distributed in plain or piedmont areas. There are 92 species and 18 varieties of local and semi-local endemic species of seed plants, accounting for 11.3% of all seed plants in this area. Eleven species are associated with endemic communities that are found in the Helan mountainous area and plain or piedmont areas. The flora of this region is a mix of both ancient and young species and exhibits clear spatial differentiation. Most endemic taxonomic groups in the plains are considered to originate from old arid regions, whereas endemic taxonomic groups in the mountains are considered to have formed through recent differentiation. The area has a rich xeric biota in which the xeric types account for 45% of all mountainous endemic plants as well as 78% of all plain endemic plants. Our study provides the first comprehensive, occurrence-based synthesis of endemic plant diversity and spatial differentiation in the East Alashan–Ordos Dryland, highlighting its long under-appreciated conservation value.

1. Introduction

Drylands occupy 41% of Earth’s land surface and support over two billion people [1]. Although deserts often exhibit lower species richness than humid regions, their floras can show pronounced local endemism shaped by strong environmental filtering, which also makes them especially vulnerable to climate change and human disturbance [2,3]. Robust conservation planning in such systems therefore depends on standardized, region-wide biodiversity inventories that can reveal endemic hotspots and diagnose spatial gaps in existing knowledge.

Global conservation frameworks—including the Centres of Plant Diversity (CPD) and, more recently, the Kunming–Montreal Global Biodiversity Framework (GBF)—increasingly translate the protection of plant-rich and endemic areas into time-bound, measurable targets such as “30 by 30” by 2030 [4,5,6]. Yet drylands remain disproportionately under-protected, with protected-area coverage substantially lower than that in non-drylands and particularly large shortfalls across Asia [7]. Closing this protection gap requires credible regional baselines that quantify plant biodiversity status and guide where conservation and future surveys should be prioritized.

The Alashan–Ordos dryland lies in a major transition zone between the Afro–Asian desert belt and the Eurasian steppe and is recognized as one of China’s eight biodiversity centers [8] and the only one located in China’s arid and semiarid regions [9]. Along a pronounced mountain–plain gradient, the Helan Mountains and adjacent ranges support many young and range-restricted taxa, whereas surrounding plains retain numerous ancient endemic elements that have been hypothesized to include relict arid lineages linked to the Tethys–Tertiary flora [10]. Botanical knowledge of the region can be traced back to late-nineteenth-century expeditions by Russian and European explorers, which produced scattered notes and specimen-based records [11]. Since the mid-twentieth century, Chinese botanists have substantially expanded research on vascular plant floras [12], vegetation [13], and landscapes or geomorphology [14]. Nevertheless, biodiversity information across the region remains spatially patchy and methodologically heterogeneous, and a standardized synthesis spanning major geomorphic units is still lacking. Consequently, it remains difficult to perform large-scale comparative analyses or to pinpoint conservation priorities with statistical confidence.

To address these spatial and methodological inconsistencies, we conducted systematic field surveys across the Alashan–Ordos region from 1998 to 2024. By employing a standardized sampling protocol, we compiled a comprehensive dataset encompassing vascular plant species composition, community types, and spatial distributions. Specifically, our objectives are (a) to provide a region-wide overview of vascular plant biodiversity across major geomorphic units; (b) to analyze the composition and spatial differentiation of endemic taxa along the mountain–plain gradient; and (c) to identify endemic hotspots, thereby establishing a baseline for biodiversity assessment and conservation prioritization in East Asian drylands.

2. Materials and Methods

2.1. Study Area

2.1.1. Alashan–Ordos Plateau

The Alashan–Ordos Plateau is located mainly in western Inner Mongolia, China, within a typical arid zone (Figure 1). It is bounded by the western fringe of the Mowushu Sandy Land to the east, the western fringe of the Badanjilin Desert to the west, the northern side of the Qilian Mountains to the south, and the Mongolian Desert and the southern fringe of the Gobi Altai Mountains to the north. The region extends across 37–41° N and 101–107° E and covers ~230,000 km². Geomorphologically, it occupies the southwestern sector of the Mongolian Plateau and is characterized by an alternating desert–mountain landscape. Major dune fields, including the Tenggeli, Wulanbuhe, and Kubuqi deserts, broadly spread across the plateau and generally trend from southwest to northeast, while Gobi surfaces are dominant in the northwest. The Yellow River flows through the region from south to north and, together with the Helan Mountains, forms a major natural boundary: the western Ordos desert and Ordos steppe occur to the east of the Helan–Yellow River corridor, whereas the Alashan desert system lies to the west.

Regional soils are mainly pale brown calcareous soil, pale gray calcareous soil, and gray desert soil; sandy soils occupy large areas, and saline–alkaline soils are also widespread. Climatically, the plateau represents a transition from a mid-temperate to a warm-temperate regime. Mean annual temperature ranges from 6.4 to 8.6 °C, with mean temperatures of 22.4–25.5 °C in July (warmest month) and −9.0 to −15.7 °C in January (coldest month). Mean annual precipitation is 50–210 mm and decreases from southeast to northwest, with rainfall concentrated in summer (July–September), accounting for 55–70% of the annual total. Along this precipitation gradient, zonal vegetation changes regularly: the eastern part (western Ordos Plateau) is dominated by desert steppe communities composed of Reaumuria soongorica, Salsola passerina, or Caragana tibetica with perennial herbs, as well as desert steppe dominated by Stipa breviflora or S. glareosa; in contrast, the western and northern parts are typical desert characterized by sparse communities dominated by Reaumuria soongorica and Nitraria sphaerocarpa [14].

2.1.2. Helan Mountains

The Helan Mountains form the most prominent topographic high along the eastern margin of the Alashan–Ordos Plateau and exhibit strong vertical differentiation in both soils and vegetation. Mountain soils show clear elevational zonation, with gray-brown soils and alpine shrub–meadow soils occurring on mid-high and sub-high mountains. Climatic conditions become markedly cooler and wetter with elevation: above 3000 m, mean annual temperature is approximately −0.8 °C and annual precipitation reaches ~430 mm; at peaks higher than 3500 m, annual precipitation is ~500 mm, mean annual temperature declines to about −2.8 °C, and the frost-free period is only 60–70 days. Vegetation is clearly differentiated by elevation and by shady–sunny slopes, and can be divided into four elevational belts: (i) front-mountain desert and desert steppe (<1600 m), (ii) piedmont and low-hillside steppe (1600–1900 m), (iii) mid-elevation to subalpine coniferous forest (1900–3100 m), and (iv) subalpine to alpine scrubby meadow (>3100 m). In the low-hillside belt, steppe communities mainly occupy sunny slopes, whereas shady slopes are dominated by mesophilous shrubs; in the mid-elevation zone, shady slopes are primarily characterized by Picea crassifolia, while sunny slopes are more sparsely covered by Ulmus glaucescens and Juniperus rigida woods together with other mesophytic shrubs. At higher elevations, shady–sunny differentiation becomes less distinct and alpine shrubs (e.g., Caragana jubata and Salix cupularis) prevail [10].

2.2. Field Sampling Methods

Floristic field surveys were conducted during the peak growing season (May–October) from 1998 to 2024. This multi-decadal survey period was essential to ensure a comprehensive and representative floristic inventory, as it accounts for the extreme inter-annual climatic variability characteristic of drylands. By extending the observation window, we successfully documented ephemeral and rare species that only emerge during sporadic high-rainfall years, which would otherwise be missed in short-term assessments. At each sampling location, we recorded geographic coordinates (GPS), elevation, landform type, slope/aspect, and a brief description of habitat and substrate. All taxonomic data were subjected to rigorous verification. Specimen identifications were performed by taxonomic experts, and all scientific names were systematically cross-checked and standardized against the Flora Innermongolica (3rd Edition). This rigorous validation process, grounded in expert knowledge and the most authoritative regional botanical record, ensured taxonomic consistency and accuracy across the entire 26-year survey period.

To capture the primary geomorphic–habitat contrast, the study area was stratified into two strata: mountain and plain/piedmont. The allocation of 115 mountain sites and 632 plain/piedmont sites (Figure 2) was proportional. Given that the vast basins and desert plains constitute over 80% of the Alashan–Ordos region and exhibit highly patchy plant distributions, this higher sampling density was essential to achieve a comprehensive and representative floristic inventory. In contrast, the mountain sites were strategically selected to encompass the full range of vertical vegetation zonation. At each site, sampling effort was allocated by vegetation layer using standardized plot sizes. In mountain sites, plot sizes were 20 m × 30 m for the tree layer, 10 m × 10 m for the shrub layer, and 1 m × 1 m for the herb layer. Shrub and herb layers were typically surveyed using three replicated plots, while the tree layer was surveyed using a single 20 m × 30 m plot. In plain/piedmont sites, sampling focused on shrub (10 m × 10 m) and herb (1 m × 1 m) layers, with replication performed whenever feasible. In extremely arid sites where the herb layer was absent or sparse, this was recorded accordingly to ensure data integrity.

Floristic composition was summarized using descriptive statistics (numbers and proportions of families, genera, and species; frequencies of endemic categories, life forms, and ecotypes) for the full region and by stratum. Spatial differentiation between strata was evaluated using occurrence-based (presence/absence) summaries, including stratum-level richness and endemic richness, and counts of shared versus unique taxa. Georeferenced occurrences of endemic taxa were further mapped in GIS to visualize spatial patterns and stratum contrasts.

2.3. Data Analysis

To compare endemicity between geomorphic strata, each taxon was classified as endemic or non-endemic within each stratum, and the endemic proportion was calculated as p = endemic/total. Differences in endemic proportions between mountainous areas and plain/piedmont areas were evaluated using a two-proportion test (Pearson’s χ² approximation with Yates’ continuity correction), implemented in R with ‘prop.test()’. Statistical significance was assessed at (p < 0.05).

3. Results

3.1. General Status of Plant Biodiversity

The Alashan–Ordos Dryland is situated in an arid region, which may be thought of as being scarce in plant species. However, the existence of the Helan Mountains has greatly enriched the regional biodiversity. There are 92 families, 382 genera, 942 species, and 32 varieties of wild vascular plants recorded in the area. Of these, ten families, 11 genera, and 18 species belong to pteridophytes, three families, five genera, 11 species, and one variety are gymnosperms, and 79 families, 366 genera, 913 species, and 31 varieties are angiosperms. The families with the highest species richness are Compositae (43 genera and 124 species) and Gramineae (44 genera and 110 species), followed by Fabaceae (19 genera and 78 species), Chenopodiaceae (20 genera and 68 species), Rosaceae (14 genera and 49 species), Ranunculaceae (12 genera and 40 species), Cruciferae (18 genera and 35 species), Cyperaceae (eight genera and 32 species), Caryophyllaceae (11 genera and 29 species), Polygonaceae (seven genera and 25 species), Liliaceae (seven genera and 25 species), Labiatae (13 genera and 19 species), Gentianaceae (eight genera and 17 species), Scrophulariaceae (eight genera and 17 species), Zygophyllacese (six genera and 16 species), Apiaceae (11 genera and 15 species), Boraginaceae (ten genera and 15 species), Salicaceae (two genera and 13 species), Tamaricaceae (three genera and 12 species), and Primulaceae (four genera and 11 species). The first 20 families account for 70.5% of all genera and 80.0% of all species in the area. The plants mainly grow in the Helan Mountains and the surrounding mountainous area. In the Helan Mountains, there are 87 families, 357 genera, 788 species, and 30 varieties of wild vascular plants. Of these, there are ten families, 11 genera, and 18 species of pteridophytes, three families, five genera, and eight species of gymnosperms, and 74 families, 341 genera, and 762 species of angiosperms (Figure 3).

3.2. Plant Endemism and Spatial Distribution

3.2.1. Endemic Species and Their Distribution

There are 92 local endemic species, Alashan–Ordos endemic species. There are also 18 local endemic varieties of seed plant species, accounting for about 11.3% of total seed plant species in the study region (including varieties). Of these, there are as many as 75 endemic species and 18 varieties that are distributed in Alashan–Ordos, especially focused in eastern Alashan-West Ordos. With Alashan–Ordos as the distribution center, the whole distribution area may extend eastward to the northern part of the Wulanchabu Plateau, westward to Ejina and the Qaidam Basin in Qinghai Province, or to the surrounding mountainous area of the study region, such as the Qilian Mountains, the Hegang Mountains, and the Xinglong Mountains in Gansu Province. The species can be called quasi-endemic to the local region with a species richness of 17 (Table S1).

These endemic and quasi-endemic species belong to 35 families and 78 genera. The Fabaceae family has the largest number of species (with 17 species and one variety). The families that follow in number are Compositae with 14 species and four varieties), Caryophyllaceac with seven species, Chenopodiaceae with six species and two varieties, Cruciferae with five species, Ranunculacea with four species and one variety, seven families that have three to four species (including varieties), five families that have two species, and another 17 families with only one species each.

These endemic species may be divided into two types. One type is the endemic species and their varieties in mountainous area, which are 60 species (16 varieties) in total and account for 54.5% of all endemic species. Those concentrated in the Helan Mountains and distributed in the Albas, Langshan, and Yabulai Mountains are 50 species in number (16 varieties). Of these, there are 31 species in the Helan Mountains, 2 species in the Langshan Mountains, 2 species in the Yabulai Mountains, and 2 species in the Aerbas Mountains. The other 13 species (1 variety) are common ones in the Halan Mountains and surrounding mountainous areas. The distribution area of the other 10 species can extend to the outer mountainous area of the studied region, with the Helan Mountains as the distribution center (Figure 4). The second category comprises plain-endemic species and their varieties, which primarily represent paleo-endemic (relict-like) elements and are entirely restricted to the plains (Table S2). There are no endemic species shared between the mountain and plain/piedmont areas. There is a significant difference in the occurrence probability of endemic taxa between the mountain and plain/piedmont areas: 46.96% in mountains versus 28.96% in plain/piedmont areas (p < 0.001) (Figure S1), indicating that mountain endemics are significantly more likely to occur at the site level. Meanwhile, because the total species richness in the plain/piedmont areas is lower than that in the mountains, the proportion of endemic taxa is significantly higher in the plain/piedmont areas than in the mountains areas (p < 0.001) (Figure 4).

The annual precipitation is only 50–210 mm in the eastern Alashan, and western Ordos. There are high mountains with over 3000 m in elevation like the Helan Mountains. Almost 90% of species, greatly enriching the biodiversity of the area, increase the proportion of Mesophyte types to 48.1%. Xeric types account for the other 51.9%. There are 788 species of plants in the Helan Mountains, including their 30 varieties, but xeric species account for 33%. Therefore, it can be concluded that the flora in the region has great xeric features for a temperate desert.

Due to the long-term insulated evolution in a xeric environment, there have been endemic xeric genera with distinctive features. Of all the endemic plants, xeric ones account for 60%. Of 60 endemic mountainous species, the life forms include small arbors, shrubs, semi-shrubs, perennial herbs and annual herbs, accounting respectively for 10%, 6.7%, 3.3%, 78.3% and 1.7% of the endemic mountainous species. The mesic types include super-xerophyte, xerophyte, meso-xerophyte, xero-mesophyte, and mesophyte plants, accounting respectively for 5.0%, 30.0%, 10.0%, 10.0% and 45.0% of the endemic mountainous species. The xeric types, composed of super-xerophyte, xerophyte, and meso-xerophyte plants, account for 45% of endemic mountainous species. Therefore, nearly half of the endemic mountainous species are xeric types, and most of them are perennial herbs. Of 50 endemic plain species that are distributed on the surface of plain/piedmont areas, the life forms are mainly shrubs, semi-shrubs, perennial herbs, and annual herbs, accounting respectively for 24%, 8%, 42% and 26% of endemic plain species. The mesic types are mainly intense super-xerophyte, xerophyte, meso-xerophyte, xero-mesophyte and mesophyte plants, accounting respectively for 20%, 56%, 2%, 10% and 12% of endemic plain species. The xeric types, composed of super-xerophyte, xerophyte, and meso-xerophyte plants, account for 78% of endemic mountainous species. Therefore, endemic plain species are mainly xeric or super-xeric perennial herbs and shrubs, of which mesophyte plants are all annual herbs (Table S1).

3.2.2. Endemic Genera and Their Spatial Distribution

The seed plants of the area have no endemic family and only one endemic subfamily, Tetraenoideae in Zygophyllacese. Reflecting the strong relictual nature of the regional flora, there are 14 endemic genera characterized by taxonomically isolated and simplified structures. There are five local endemic genera distributed mostly in the study area. There are also two endemic genera whose distribution centers are within the study area (nearly local endemic genera). In addition, there are seven endemic genera that are primarily distributed in northern China (

Table 1. Endemic genera of plants in the Alashan–Ordos drylands.

Endemic Genera	In Family	Number of Species (Local/Genus)	Endemic Type	Distribution
Tetraena	Zygophyllacese	1/1	Local, West Ordos	West Ordos
Potaninia	Rosaceae	1/1	Local, East Alashan—West Ordos	East Alashan–West Ordos
Tugarinovia	Compositae	1/1	Local, Alashan–Ordos	Alashan–Ordos
Stilpnolepis	Compositae	1/1	Local, Alashan–Ordos	Alashan–Ordos
Pugionium	Cruciferae	3/4	Local, south Mongolian Plateau	Sand lands in south Mongolian Plateau
Ammopiptanthus	Fabaceae	1/2	Nearly local, Gobi desert in Mid-Asia	Gobi desert in Mid-Asia
Elachanthemum	Compositae	2/2	Nearly local, Gobi desert in Mid-Asia	Gobi desert in Mid-Asia
Ostryopsis	Betulaceae	1/2	Chinese	North–Southwest China
Yinshannica	Cruciferae	1/8	Chinese	North to Southwest China
Plagiopspermum	Rosaceae	1/3	Chinese	North to Southwest China
Speranskia	Euphorbiaceae	1/3	Chinese	North to Southwest China
Xanthoceras	Sapindaceae	1/1	Chinese	North and Northeast China
Xanthopappus	Compositae	1/1	Chinese	Northwest to Southwest China
Anemarrhena	Liliaceae	1/1	Chinese	North to Southwest China

). These genera are monotypic, which contain only one species, or oligotypic genera, which contain less than ten species in every genus. The genera of Tetraena, Potaninia, Tugarinovia, and Stilpnolepis are all endangered and have small distribution areas. In particular, the distribution areas of Tetraena are very limited, existing only in the western verge of West Ordos. The five local endemic genera and two nearly local endemic genera are all distributed in plain/piedmont areas rather than randomly distributed inside the mountainous areas. There are the only Chinese endemic genera in the Helan Mountains and the surrounding mountainous areas (Table 1).

3.2.3. Endemic Communities and Their Distribution

The distribution of endemic plants in the Alashan–Ordos dryland is quite non-uniform in space. Some plants, for example Acer stenolobum var. Megalophyllum, are very few in number, and therefore can rarely form communities. There are only two endemic species in the mountainous area and eight endemic species in the plain/piedmont areas that form endemic plant communities. Forms of Leptodermis ordosica and Hippolytia alashanensis are mountainous endemic communities. Forms of Ephedra rhytidosperma, Tetraena mongolica, Helianthemum ordosicum, Potaninia mongolica, Prunus mongolica, Ammopiptanthus mongolicus, Reaumuria trigyna, and Brachanthemum gobicum are plain endemic communities.

4. Discussion

4.1. The Foundation to Establish a Biodiversity Center

The five endemic genera and two nearly endemic genera serve to establish the area as the biodiversity center in the arid region of northwestern China. According to the classification system proposed by Wang and Zhang [8] of the Center of Seed Plant Abundance in China, there are eight biodiversity centers in China and only two are north of the Qinling Mountains and Huaihe River. One is the Zhongtiao Mountains—Southern Taihang Mountains area and the other is the Southern Mongolia Center (Alashan–Ordos center). The former is the area in which the endemic genera of China’s warm temperate zone are aggregated and is the northern border by which the southwestern and southern endemic genera are divided. It is therefore similar to the Qingling center in many aspects. There are more than 40 endemic seed plant genera in China, but few endemic genera in the local region exist, and most of the genera are northern extensions of endemic plants from southwestern China. As for the Zhongtiao Mountains–Southern Taihang Mountains area, there are only two endemic genera: Taihangia in the Rosaceae family and Opisthopappus in Compositae. But in the Alashan–Ordos center, there are seven endemic and nearly endemic genera. This makes it the “hot spot” of endemic genera in northern China with unique biodiversity characteristics. This may result from elevationally driven climatic zonation, acting in concert with microtopographic processes—such as slope aspect, slope position, topographic shading, and cold-air pooling—to generate highly heterogeneous hydrothermal conditions and microrefugia, thereby facilitating the persistence and aggregation of endemic taxa in arid mountain systems [15]. This is consistent with findings from the Namib Desert: despite hyper-aridity, distinctive and endemic-rich biota can be maintained, partly supported by fog-derived moisture and geomorphologically isolated habitats [16]. Similarly, among North American deserts, the Chihuahuan Desert is often recognized for exceptionally high diversity and endemism. Its landscape “insularity”—created by the compartmentalization of desert basins and surrounding mountain systems—is widely considered to promote the persistence and accumulation of endemic plant taxa; estimates suggest that the flora comprises ~3500 species, of which about one third are endemic [17].

4.2. Remnants of Ancient Endemic Genera in the Plain Area

Our results indicate that the endemic and near-endemic genera of the Alashan–Ordos dryland are disproportionately concentrated in the plain/piedmont areas, forming a distinctive “relict-like” component of the regional flora. In the local endemic genus set, four genera are monotypic (Tetraena, Potaninia, Tugarinovia, and Stilpnolepis), while Pugionium contains only a few species. The two quasi-endemic genera (Ammopiptanthus and Elachanthemum) are also species-poor; notably, Elachanthemum was long treated as monotypic until a second species, E. polycephalum, was described from western Alashan. Here, the terms “relict-like/ancient” are used as biogeographic interpretations based on taxonomy, species-poor (mono-/oligotypic) lineages, and published floristic literature, rather than on a formal phylogenetic reconstruction.

Tetraena: This is a kind of intense xerophyte shrub with a unique shape. Its position in system classification is hard to determine, and scholars usually temporarily place it in Zygophyllacese. Ma [18] argued that it was genetically related to plants in the Zygophyllacese family, but was still different in many aspects. Therefore, it was proposed that it should belong to Tetraenoideae, which has only one genus and one species, showing its isolation in system evolution. It is distributed only in a narrow and long region from the eastern side of the northern piedmont of the Helan Mountains to West Ordos in the western piedmont of the Albas Mountains (Figure 2). Accordingly, its distribution area is limited, and the area where the community may be formed is even more limited. Therefore, it is a geographically remnant genus and is the “living fossil” of plants in arid areas in northwestern China. However, its system position, origin, and evolution still deserve more in-depth research.

Ammopiptanthus: This is a kind of evergreen super-xerophytic shrub and also the only kind of evergreen shrub in Asian temperate deserts (Figure 2). There are only two species in it. One is Ammopiptanthus mongolicus in the western part of Alashan and Ordos, and the other is A. nanus in a very narrow region between the southwestern part of the Tarim Basin in Xinjiang, the northern piedmont of the Kunlun Mountains, and the western Tianshan Mountains (Kyrgyzstan). J. Maximowicz initially placed it in Piptanthus, an ancient evergreen plant in the Himalayas, but Popov [19] suggested that it was related to Podolyria, an evergreen plant in South Africa. Cheng [20] also claimed that Ammopiptanthus had the unique feature of a xerophyte, and was far from Piptanthus, but was genetically close to Podolyria of South Africa. However, it is not from a genetically close ancestor, instead belonging to a remnant species of subtropical xerophyte evergreen broadleaved forest from the Tertiary Period.

Potaninia: This is a kind of super-xerophytic shrub (Figure 2). It is a genus with a unique feature in the family of Rosaceae, based on the feature of its three base flowers. Potaninia is a genus with single species Potaninia mongolica Maxim.; its phylogenetic status is still argued today. Some researchers [21] found that it was related closely with Cliffortia from South Africa, while Zhao Yi Zhi pointed out Dasiphora from East Asia is the closest genus with Potaninia [22]. Petals and Calyxes of Potaninia are usually three, but are sporadic four or five on the several plants in the rainy years. In particular, its leaves are very small and fall outright in the rainless summer. These traits are likely the result of adapting itself to the dry climate of the desert long-term, and Potaninia is maybe an age-old and remnant genus in the Alashan desert.

Tugarinovia: This is a kind of super-xerophytic perennial herb with a primitive and unique shape (Figure 2). Additionally, the features of females and males are located on different plants, which is very rare in Compositae. It was formerly misplaced in Inuleae, but is now assigned to Cynareae. It also probably originated from Atractylodes in the eastern Asian biota [23].

Furthermore, Stilpnolepis and Elachanthemum are two single-species genera evolving from Artemisia. They are two very close sister genera, and some scholars have even combined them into one genus [24]. Because their inflorescence grows singly on top of the plant, they are two ancient types closely related to Artemisia and may originate from ancient Artemisias genera in northern Laurasia [22]. There are slightly more species in Pugionium, and generally it is believed that there are four species in the genus. Except for one species, which is distributed in Mongolia, the other three species are all in Alashan–Ordos. It takes up a unique position in Cruciferae, so it is very difficult to determine its position in Phylogenetic Classification. Some scholars put it into different sub-families, and there has not been a proper position for it, nor has any genetically close genus been found.

Based on the above analysis, it can be inferred that the plateau plants in Alashan–Ordos are very ancient. Wu et al. [25] suggested that Chinese endemic genera originate mainly from the Tertiary Period in the North Pole, during the Tertiary Period in the ancient Tropical Zone (the Tertiary Period in Gondwana), and during the Tertiary Period in the ancient Mediterranean region. Additionally, most of the xeric endemic genera of the region probably originated from the Tertiary Period in the ancient Mediterranean region as well.

Some species, for example Ephedra rhytidosperma, Tetraena mongolica and Helianthemum ordosicum, whose distribution areas are very small, are close to disappearing because of climate change and urban growth.

4.3. Variation in New Endemic Plants in Mountainous Areas

The stark contrast between mountain neo-endemics and lowland paleo-endemics highlights the dual role of the Alashan–Ordos region as both a museum and a cradle for dryland biodiversity. The Helan Mountainous area is the divergence center for the new endemic plants. Of 16 species and 15 varieties, the plants display strong modern divergence. For example, Acer stenolobum var. megalophyllum and Acer stenolobum var. pubescens are the arid varieties of A. stenolobum. They are scarce in number, and the original species are also very scarce in the Helan Mountains. The other endemic species that are only distributed in the Helan Mountains (e.g., Urtica helanshanica, Melandrium alaschanicum, Melandrium auritipetalum, Pseudostellaria helanshanensis, Stellaria bistyla, Anemone alaschanica, Delphinium mollipilum, Oxytropis holanshanensis, Saussurea alaschanica) and the endemic species that are distributed in both the Helan Mountains and the surrounding mountainous area, with Helan Mountains as the center (e.g., Rheum racemiferum, Rh. Uninerve, Silene ningxiaensis, Stellaria alaschanica, Scrophularia alaschanica and Leptodermis ordosica) for the most part are clearly modern diverged. Among them, there are some species that have formed geographical replacement distributions.

For example, Leptodermis ordosica is the replacement for L. oblonga, and Scrophylaria alashanica is the replacement for S. moellendorffii. The species Seseli langshanense and Dracocephalum rigidulum from the Langshan Mountains, Saussurea jurineioides and Saussurea yabulaiensis from the Yabulai Mountains, and Allium alabasicum and Ajania alabasica from the Alabas Mountains also apparently diverged in genera during modern times.

The variations in the new endemic genera in the Helan and nearby mountains are closely related to the long-term isolated evolution in the area. Deserts surround these mountains, while the mountains—especially the high Helan Mountains—have higher precipitation that cause them to become “islands” in the landscape. This not only enriches the biological diversity of the area but also promotes variations in new genera due to the relatively closed environment. Even the Yabulai Mountains, which are below 2000 m in elevation and lie between two deserts with annual precipitation of less than 100 mm, have greatly increased the biodiversity and formed the endemic genera in the local region. At present, there are two endemic species that have been identified. In recent years, we have discovered that there are still a few species whose names cannot be determined, so it is possible that they are unknown new genera. In addition, the Yabulai Mountains may become the modern “refuge” for some arid plants. For example, Chesneya grubovii, a species in the Fabaceae family, is an endemic species in the Gobi. Prior to the 1980s, it could be found in the Alashan desert area and the Helan piedmont. Since then, especially during several large-scale explorations after the 1990s, the species has never been located in the above-mentioned areas. In 2004, a few individual plants of the species were found on remote isolated mountains of the Yabulai range.

4.4. Conservation Gaps and Recommendations

Spatial analysis reveals significant structural deficiencies in the current protected-area network for safeguarding regional endemic diversity. Although the core of the Helan Mountains has been designated as a National Protected Area, protection is largely confined to high-elevation zones, leaving prominent gaps in the species-rich piedmonts and low-elevation transitional areas [26]. To further quantify this shortfall, we assessed protected-area coverage for five representative endemic plants. The results show that only Tetraena mongolica shows relatively high PA coverage, largely because a dedicated reserve has been established specifically to protect this species, resulting in 65.49% of its distribution falling within existing protected areas. In contrast, the other four endemic plants lack species-targeted protected areas, and each has a coverage rate below 30%, indicating pronounced species-level imbalance and conservation gaps in the current PA network. At the regional scale, 64.44% of species distributions remain outside the current protected-area system, indicating that the existing network provides insufficient coverage of endemic plants and their key habitats (Table S3; Figures S2–S7). These findings highlight an urgent need to improve conservation effectiveness through boundary optimization and integration of protected areas (Figure 5).

Based on these findings, this study proposes two targeted recommendations: first, the conservation boundaries of the Helan Mountains should be re-evaluated and expanded, shifting from “core-peak protection” to an integrated “mountain–plain buffer management” that encompasses low-elevation transitional zones to protect xeric endemics distributed at lower altitudes. Second, for quasi-endemic species and relict genera in plain areas, it is urgent to integrate existing provincial-level protected areas to reduce habitat fragmentation [27]. Long-term monitoring networks should be established specifically for sampling sites heavily disturbed by anthropogenic activities, thereby providing a robust scientific baseline for biodiversity assessment in East Asian drylands [28].

5. Conclusions

The Alashan–Ordos dryland supports a remarkable assemblage of xeric plant taxa that are endemic to Chinese arid regions and, more broadly, to the arid zone of temperate Asia. Based on authoritative floras (e.g., regional floras) combined with long-term field surveys, we provide a standardized checklist and summarize clear spatial differentiation of endemic taxa along the mountain–plain/piedmont gradient. The main conclusions are as follows:

(1)

There is an endemic sub-family (Tetraenoideae), 5 endemic genera (Tetraena, Potaninia, Tugarinovia, Stipnolepis, and Pugionium), and 2 endemic genera from mid-Asian deserts (Ammopiptanthus and Elachanthemum). The 6 endemic or quasi-endemic genera in the region are all located in high plain or piedmont areas.

(2)

There are 92 endemic or quasi-endemic seed plants in the local region and 18 varieties, accounting for 11.3% of the area’s plants. Of these, 60 species (including varieties) are in mountainous areas and 50 in plain or piedmont areas.

(3)

There are 10 species that may form endemic communities. Of these communities, there are three in the Helan Mountains: the Leptodermis ordosica community in Mongolia, and the Hippolytia alashanensis community in the Helan Mountains. There are also eight communities in plain or piedmont areas: the Ephedra rhytidosperma community, the Tetraena mongolica community, the Helianthemum ordosicum community, the Potaninia mongolica community, the Prunus mongolica community, the Ammopiptanthus mongolicus community, the Reaumuria trigyna community, and the Brachanthemum gobicum community.

(4)

The endemic flora of the area is both ancient and young, and also exhibits strong xeromorphism (xerophytes: 45% in mountains vs. 78% in the plain or piedmont areas). Most endemic taxa in the plain or piedmont areas are ancient elements inferred from taxonomic literature and distribution patterns, whereas endemic taxa in the mountains are mainly narrow-range young elements.