Liverwort and Hornwort Flora of Hoàng Liên National Park and the Adjacent Areas (North Vietnam, Indochina)

The study of the flora located in the central part of the Hoàng Liên Sơn Range in the northern region of Indochina has revealed 279 species of liverwort and hornwort, 26 of which are newly reported for the flora of Vietnam. The uniqueness and peculiarity of the studied flora are explained by the significant altitudinal range in the area treated and its position in the contact zone of the Sikang-Yunnan floristic province of the East Asian Floristic Region with the Indochina Floristic Region. The checklist includes data on the distribution of each species in the studied region, habitats, and accompanying taxa. The high disunity of the regional floras of the southern tip of the East Asian region compared to the lesser disunity of the regional floras in the north of the East Asian region is shown. In general, the studied flora possess Sino-Himalayan mountain subtropical characteristics with the large participation of tropical elements.


Introduction
The Hoàng Liên Sơn Range, stretching ca. 180 km, is located in the northern part of Vietnam and is an orographic continuation of the Hengduan Mountains, ranging from the southeastern edge of the Tibet Upland to Indochina. The system of the mountain ranges of Northern Vietnam is a site of penetration of the Sino-Himalayan flora to the south [1,2] and a zone of interpenetration of the mountainous subtropical flora of the Sikang-Yunnan floristic province and the tropical flora developed in the lowlands. The mixing of different floral elements and the significant altitudinal differences (to 3143 m a.s.l.) contribute to the formation of the peculiar and taxonomically rich flora in different taxonomic groups. As Averyanov et al. ([3]: 35) pointed out, "Approximately 15.3% of Vietnamese endemics occur in the Vietnamese portion of the Sikang-Yunnan Province", and this is only one of the peculiar features of the area. The second noticeable feature worth mentioning here is the great variety of rock compositions in the Hoàng Liên Sơn Range, which vary from acid granites to distinctly alkaline limestone raised up to 1800-2000 m a.s.l. The special phytogeographic importance of the region inside Indochina, including the highest point in Indochina, elicits interest in the study of the Hoàng Liên Sơn Range. The liverworts of the Hoàng Liên Sơn Range were studied fragmentarily, summary data were never published, only scattered floristic findings were disseminated across various papers, and the distribution of species in taxonomic treatments was mentioned [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Moreover, for Northern Indochina, there are no published summary lists for any local flora at all. Even excluding Laos, where information about liverworts is generally fragmentary [18], the well-studied areas [19] where much work has been carried out-for example, in the Doi

Checklist
Taxa in the checklist are in alphabetical order; nomenclature follows Söderström et al. [20], with the exception of Solenostomataceae, where the narrow genus concept was adopted [21], and for new concepts of taxa in Calypogeia and Chiastocaulon according to Bakalin et al. [10] and Patzak et al. [22], respectively. Each species is annotated by the following scheme: (1) species name, (2) altitude(s) where the species was collected, (3) brief description of habitat, (4) numerals of collecting localities in accordance with that described in the Section 4.1 of the paper, (5) selected field numbers (by one per locality), (6) accompanying species if any (questionable identifications are omitted), (7) brief citation of literature reports-where present (the spelling of geographic names corresponds to those in cited literature), literature reports by the authors of the present paper are only referenced, but not annotated, and the literature sources are referenced in square brackets, (8) taxonomic comments, if any. The species newly recorded for Vietnam are marked with an asterisk.

Altitudinal Trends in the Formation
The distribution of the altitudinal floral fragments by a 100-m gap on the DCA diagram ( Figure 1) shows an almost even distribution of floras across the diagram. The visual proximity in Figure 1 of altitudinal belts >2800, >2900, >3100 is not actually real, as follows from the table of distances between floras of the mentioned altitudinal zones (Tables 2  and 3) due to underestimations in third axis distances. In general, the value in the x-axis is almost clearly inversely proportional to the elevations: the floras are distributed from the highest to the lowest. According to the distance table (Table 3), the distances between floras gradually increase as the difference between the elevations increases. There are, however, deviations from this rule. For example, flora in the >2200 range is more closely related to the floras of the low altitudinal belts than even the lower-lying floras >2000 and >2100. The floral fragment >2200 is quite unique, and its relationship with the flora >1800 is generally the closest of all the range floras involved in the analysis. In general, compared to the average distances, distances above average are observed for altitude differences of more than 1000 m. lated to the floras of the low altitudinal belts than even the lower-lying floras >2000 and >2100. The floral fragment >2200 is quite unique, and its relationship with the flora >1800 is generally the closest of all the range floras involved in the analysis. In general, compared to the average distances, distances above average are observed for altitude differences of more than 1000 m.    The distribution of altitudinal floral fragments with 200-m gaps ( Figure 2) generally shows the same characteristics. At the same time, due to the averaging effect, the average distances for this matrix (Tables 4 and 5) are lower than the average distances between floras specified over 100-m segments. The highest distances (a hundred conventional units exceeding the distances between any other flora) are the distances between the lowest altitude level (>1200) and the highest (>2800, >3000) ( Table 5).

Floristic Connections of Studied Area with Other Floras
The obtained DCA diagram ( Figure 3) includes all eight floras: four territorially close at the southern tip of the East Asian region (including the studied area) and four from its northern tip and the middle part of Pacific Northeast Asia. Clear clusters are not distinguished on the diagram, and the position of the floras on the abscissa axis is directly proportional to the increasing latitude, although the distribution is not even and a significant difference in latitude may not be reflected in an equally significant difference in x-axis distance.

Floristic Connections of Studied Area with Other Floras
The obtained DCA diagram ( Figure 3) includes all eight floras: four territorially close at the southern tip of the East Asian region (including the studied area) and four from its northern tip and the middle part of Pacific Northeast Asia. Clear clusters are not distinguished on the diagram, and the position of the floras on the abscissa axis is directly proportional to the increasing latitude, although the distribution is not even and a significant difference in latitude may not be reflected in an equally significant difference in x-axis distance. For each group of floras, distances in kilometers (Tables 6 and 7) and distances in conventional units (Tables 8 and 9) from the results of a three-dimensional distribution obtained by DCA were determined. Since all eight floras were included in one matrix, direct comparison of DCA distances in the two groups is possible.   For each group of floras, distances in kilometers (Tables 6 and 7) and distances in conventional units (Tables 8 and 9) from the results of a three-dimensional distribution obtained by DCA were determined. Since all eight floras were included in one matrix, direct comparison of DCA distances in the two groups is possible.  The average distance in kilometers between the floras of the first group (Hoàng Liên plus) is 652 km. The average distance between the floras of the second group (Iturup plus) is 2122 km, which exceeds the average distance in the first group by three times. At the same time, the average distances between floras in conventional units in the first group is 271, while, in the second, it is only 200. Thus, despite larger distances in kilometers, the relationships between floras in the second group are closer. In the first group, above average distances are found between the Beihai and Hoàng Liên Sơn floras, although the distance, expressed in kilometers, is below average between them. In the second group, the above-average distance in conventional units is between the Jiri-san flora (the southernmost of those compared in the group) and two floras in Northeast Asia (Bystrinsky and Commanders), separated by more than 3000 km. At the same time, the Iturup flora, located at the northernmost tip of the East Asian region, turns out to be quite close to all other floras of the second group, despite serious geodesic distances varying from 1450 (Bystrinsky) to 2000 (Jiri-san) kilometers. Thus, there is higher disunity in floristic composition in selected floras in the south of the East Asian Floristic Region (Hoàng Liên plus) than in its northern extremity plus the middle part of Pacific Northeast Asia (Iturup plus).

Taxonomic Diversity
The total known taxonomic diversity reaches 279 species and exceeds that in the compared floras of South China. Around North Indochina, this is presumably the richest known liverwort flora. Lejeuneaceae occupies the first position in the list of the top 10 families. However, it covers only 16.5% of the total flora. According to published reports for relatively well-studied and mountainous Malaysia [30], Lejeuneaceae in that distinctly tropical mountainous country comprises 40% of the total diversity. Even more so, the comparatively low value of Lejeuneaceae is evident in the generic spectrum, where Lejeunea ranks third and Cololejeunea, with eight species, only 10th. No additional Lejeuneaceae genera were included in the leading top families in Hoàng Liên Sơn. This can be explained by two factors: (1) the insufficient study of Lejeuneaceae and (2) its objectively lower value in the mountain flora, where the mountain species of the Sino-Himalayan distribution play a significant role in its formation (among which Lejeuneaceae are not numerous). Most likely, both factors act together, which also supports the assumption that the taxonomic diversity of species known in the flora will be further increased with future targeted research. The high proportion of Sino-Himalayan species in the flora is evidenced by the high values of the genera Scapania and Calypogeia, which are generally diverse in the mountains of the Holarctic but are especially diverse in the mountain mesophytic floras of the Sino-Himalayas [31]. The Sino-Himalayan influence on the formation of the flora of Northern Vietnam was noted earlier by our group [4,8]. This also led to the conclusion that the studied flora is, although rich in tropical elements, not tropical by the general content.
Twenty-six species are reported for the first time for the flora of Vietnam (marked with an asterisk in the list). Some of them, such as Cephaloziella willisana, Jubula sikkimensis, Kurzia borneensis and Plagiochila hokinensis, have a questionable taxonomic status. Together, all new records are to be expected, taking the general distribution patterns of all novelties into account. Most of them are widespread in the Sino-Himalayas. Additionally, it is worth mentioning that some new-for-Vietnam species of Riccardia (R. glauca, R. latifrondoides, R. parvula) and Solenostoma (S. faurieanum, S. parvitextum, S. pseudocyclops, S. rotundatum) may actually be incorrectly identified and represent weakly morphologically diversified new-for-science taxa and belong to species geographically vicarious in relation to those mentioned. In addition, the same problem is estimated to occur in almost all large genera of the studied flora, although not so prominently. To resolve this issue, it is necessary to carry out special molecular genetic studies, some of which we intend to conduct in the near future. In addition, it is worth mentioning that among the mentioned genera, as well as among others, there are a number of specimens identified to the genus only (and not included in the checklist) and presumably belonging to species that are new to science. Thus, the presented list is incomplete. The exact number of species that will be additionally found after further research in the study area is difficult to predict, but it is clear that new research will increase the number of known species to no less than 30-50 taxa.

Altitudinal Trends
The greatest liverwort diversity is observed within altitudinal one-hundredth meter diapasons of 1500-1599 m a.s.l. (104 species) and 2000-2099 m a.s.l. m. (105 species). This can be partly due to random factors-for example, the stochastically greater concentration of studied localities (and, as a result, more exhaustive collection of the flora) and more time spent on research. However, at the same time, it can be noted that both of these intervals are peculiar boundaries in the altitudinal distribution of a number of taxa. For example, the diapason 1500-1599 m a.s.l. is an upper limit for Drepanolejeunea commutata, Lejeunea obscura, Lepidozia subintegra, Leptolejeunea elliptica, Mastigophora diclados, Plectocolea granulata, P. hasskarliana, P. tetragona, Saccogynidium muricellum, etc., in the area treated. The same diapason is also the lower limit for Aneura pinguis, Bazzania japonica, Calycularia crispula, Calypogeia cuspidata, C. granulata, C. lunata, C. tosana, Cephalozia hamatiloba, C. siamensis, Cylindrocolea recurvifolia, Frullania moniliata, Fuscocephaloziopsis gollanii, etc. In addition, most of the studied limestones are concentrated in this diapason, which leads to the enrichment of the flora with basiphilic species, such as Plagiochasma cordatum.
In fact, there are more species that interrupt their distribution in both diapasons, but given the unevenness of knowledge (since the primary task was to identify the general diversity and not the patterns of altitudinal distribution), it is hardly possible to carry out any statistically reliable calculations on this issue.

Relationships and Diversification with Adjacent Areas
As noted in the Materials and Methods and Results sections, the comparison with other floras has an evidently "one-sided" nature, since the studied flora is the southernmost of those compared. This is determined by the lack of representative data for the comparison of local floras in Northern Indochina. However, considering the proportion of families in the total spectrum and, especially, the generic spectrum of the studied flora, we suggest that the studied flora is also predominantly mountainous subtropical, and such a comparison seems to be possible (although certainly not ideal). A comparison of four selected floras at the southern flank of the East Asian Floristic Region showed that, despite the relatively small kilometric distances between the compared floras, the interrelationships between them are rather low. Moreover, the relationships are smaller than the relationships between the floras situated at much greater distances (in kilometers) at the northern tip of the East Asian region and even in Pacific Northeast Asia. This feature of the strong disunity of floras in the Sino-Himalayas was revealed long ago (although it has a very indirect relation to the area covered by the compared floras) and was described with the possible main trends approximately 100 years ago [32][33][34]. The fundamental difference between the mountain floras of the Alps and the Sino-Himalayas was emphasized at the same time. Ward ([34]: 73-74) wrote, "It is necessary to remember that this Himalayan-Chinese flora is not alpine in the European sense. The Alps of Europe are generally supposed to have derived some of their flora from the Arctic, but clearly the Himalaya did not, and the resemblance between the European alpine flora and the Himalayan alpine flora is only a broad resemblance, despite the fact that the mountain ranges belong to one system". The ancient features of the Sino-Himalayan flora, the absence of ice sheets in the foreseeable geological past and the close junction of the upper reaches of completely oppositely directed large rivers in the region led, so to speak, to the accumulation of uniqueness, which is largely (although far from that observed in glaciated Europe) deprived in more northerly Pacific Asian floras, even within the East Asian Floristic Region.

Area Treated Identification
The study area is located in the central part of the Hoàng Liên Sơn Range, which extends from northwest to southeast for ca. 180 km, with a maximum width with side spurs reaching approximately 30 km. The area includes the highest mountain of Indochina-Phan Xi Pang, with an elevation of 3143 m a.s.l. in its summit. The elevation in the area treated starts at approximately 1300 m a.s.l. and reaches the Phan Xi Pang Peak. The national park itself has an area of 685 km 2 (https://en.wikipedia.org/wiki/Ho%C3%A0ng_Li% C3%AAn_National_Park (accessed on 23 February 2023)) and lies within two Vietnamese provinces: Lao Cai and Lai Chau. It is worth mentioning that the study area (1) covers only a small portion of the park and (2) includes some adjacent areas that do not formally belong to the park. However, since this entire area is a single unit located on the macroslopes of the Phan Xi Pang Mt. and its adjacent spurs, there is no reason to divide the nationally protected area from those reserved on the provincial level and the non-reserved areas. Moreover, one of the most important liverwort diversity concentration points is observed in the Ham Rong municipal park located in Sapa Town. All collecting localities are listed in Table 10 and Figure 4 and distributed between 22.421 • N and 22.302 • N latitudinally and 103.767 • E and 103.848 • E longitudinally.   Table 4.

Natural Environments
Although, topographically, the Hoàng Liên Sơn Range is located on the Indochina Peninsula, geomorphologically, it has no association with the Indochina Block, which occupies the main area of Indochina. The main events that led to the formation of the Hoàng Liên Sơn Range occurred approximately 40-30 million years ago, when the collision of the

Natural Environments
Although, topographically, the Hoàng Liên Sơn Range is located on the Indochina Peninsula, geomorphologically, it has no association with the Indochina Block, which occupies the main area of Indochina. The main events that led to the formation of the Hoàng Liên Sơn Range occurred approximately 40-30 million years ago, when the collision of the Indian plate with the Asian continent caused the clockwise rotation of the Indochinese platform and "pressed" it into the South China Block [35,36]. The latter contributed to (1) the formation of folding, which is orographically expressed as a system of mountain ranges in Northwestern Vietnam, and (2) the rise of marine limestone deposits to heights reaching 2000 m a.s.l. and the opening of ancient granites and similar acidic rocks at altitudes exceeding 1500 m a.s.l. and now reaching more than 3000 m a.s.l. in Northern Indochina, with the highest point being Phan Xi Pang Mt. (3143 m a.s.l.). The formed mountain system is adjacent to the (1) Annam Mountains, located along the modern northeastern edge of the Indochina Block; (2) mountains of the Simao Block westward of the Hoàng Liên Sơn Range; and (3) the Hengduan Mountains, extending from the southeastern edge of Tibet (in the southern part, formed for the same reasons as in the mountain system of Northeastern Vietnam and described above) and contacting the Hoàng Liên Sơn Range in the northern tip of the latter [37]. Averyanov et al. ([3]: 34) wrote about this area: "Mountain systems here are generally composed of silicate rocks, mainly granite, gneiss, rhyolite or quartzite, formed as extensive magmatic intrusions of late Paleozoic and Mesozoic ages. Tertiary tectonic movements uplifted these montane terrains to modern elevations, and further erosion formed the present characteristic rocky landscape of this highland area".
Therefore, geomorphologically and phytogeographically, the mountains of the northwestern tip of Vietnam are sound continuations of the Hengduan Mountains, through which a huge number of Sino-Himalayan flora elements penetrated into Indochina. The latter, in fact, makes this region the southern outpost of the East Asian subtropical flora [1,2]. At the same time, a mosaic combination of ranges with valleys occupied by tropical vegetation in lowlands also enriches the mountain systems of Northern Vietnam with tropical species. Another factor affecting the taxonomic diversity of the Hoàng Liên Sơn Range is the presence of a wide range of chemically different rocks, for instance, evidenced by pronounced outcrops of alkaline limestones (of karst origin) and acidic granites. Finally, a great altitudinal range, with the highest exact mountain in Indochina, Phan Xi Pang, allows the development in the upper belts of special types of vegetation not represented or poorly developed in other mountain systems, even in the northern part of Vietnam. Some authors [38] generally consider the vegetation of the upper belt of the Hoàng Liên Sơn Range to be temperate, instead of mountain subtropical. The latter statement may be questioned; however, the distribution, apparently relict, as in the case of Abies delavayi Franch., indicates the presence of temperate species in the Hoàng Liên Sơn Range. Moreover, several instances of climate cooling, including the Miocene cold interval (ca. , are very noticeable [39] and should influence the deep penetration of the oro-temperate flora into Northern Vietnam. Averyanov et al. ([3]: 29) stressed the temperate features of these highland communities: "A coniferous community of distinctly temperate affinities occurs in northern Vietnam at higher elevations between 2400-2900 m in only the northwestern part of the country, with occasional dominance of Tsuga dumosa and Abies delavayi". The presumable relict occurrence of Gymnomitrion rubidum (Mitt.) Váňa, Crand.-Stotl. & Stotler, in the scattered community of Abies delavayi probably evidences that the temperate taxa that survived together (as a suite) are now alien to them, not temperate communities [9]. All of the above make the taxonomic diversity of the Hoàng Liên Sơn Range potentially high, even in comparison with other mountain systems. The earlier statistical analysis of the distribution of new records in Northern Vietnam [8] showed that the discovery of liverwort species new to the country is most likely in the upper mountain belts. The wide occurrence of Sino-Himalayan taxa in the upper belts is the most interesting and distinctive trait of the studied area.
However, in the general zonal characteristic, the dominant type of vegetation in the study area is evergreen montane and highland forests on silicate rocks at 1000-3000 m a.s.l [3]. In reality, the organization of floristic complexes is more complicated since commu-nities are also developed on alkaline substrates. Moreover, altitudinal climatic differentiation supplemented the difference in substrates. These factors result in ( [3]: 26) "a relatively sharp distinction in vegetation structure between lowland and montane forest communities. This delineation is marked by a decline in the number of taxa of tropical families such as the Anacardiaceae, Dipterocarpaceae, Euphorbiaceae, Meliaceae and Simaroubaceae and an increase in dominance of subtropical and temperate families like Fagaceae, Theaceae, Magnoliaceae and a diverse assemblage of conifers".
Due to elevations lower than 1300 m a.s.l. being absent in the studied area, we did not study the typical tropical forests developed in the lowlands of Northern Vietnam at elevations below 1000 m a.s.l. The typical landscapes and liverwort habitats are in Figure 5.
Since the studied area has mountainous relief, the climate (especially temperature) changes drastically with altitude and slope exposure. To determine the most general characteristics of the alternation of weather elements, we used the climate chart on the ClimateData website (https://en.climate-data.org/asia/vietnam/lao-cai-province/sa-pa-36229/ (accessed on 22 February 2023)) for the weather station located in Sapa Town. The station is situated at an altitude of 1489 m a.s.l. and provides features of the climate of the lower altitude level and its seasonality throughout the year in the area treated. According to the Köppen-Geiger climate classification, the climate in Sapa is temperate with warm summers and no dry season (Cfb according to the mentioned classification) [40]. Despite the term "no dry season", Sapa has significant variability in the amount of rainfall that occurs during the seasons. In addition, temperature seasonality is quite pronounced. Although Sapa is located south of the Tropic of Cancer, the alternation of temperatures over the seasons is very well expressed here. The warmest quarter of the year is June-August. This period is also the wettest. The driest quarter of the year is from November to January, and the coldest quarter is observed with a slight shift-from December to February. The warmest month is July, and the coldest month is January.
Since the coordinates were known for all our collection localities, we then obtained the bioclimates from the WorldClim database (https://www.worldclim.org/data/bioclim.html (accessed on 22 February 2023)) for each point, which made it possible to compile a general characteristic for the study area. These data are placed in Table S1 and are discussed below. To characterize each point, all 19 bioclimates were obtained, which can be determined with a maximum accuracy of 30", and if the points are closer, then the parameters could merge. Despite the inevitable averaging of the data (for example, all six highest points above 2900 m a.s.l. were combined into one cluster, and points 19 and 26, located on a steep slope, clearly show the climatic values of the upper altitude levels), the results indicate serious altitudinal differences in local climates across the altitudinal gradient. The lowest point is located at an altitude of 1325 m a.s.l., and the highest is located at an altitude of 3143 m a.s.l. The average annual temperature on this 1800-m diapason, when climbing into the mountains, gradually drops from almost 17 to 9 • C. The average maximum temperatures vary from 26 to 19.9 • C, and the average minimum temperatures range from 6.3 to -0.7 • C. The average temperature of the wettest quarter (coinciding with the warmest) varies from 21.8 to 14.0 • C, and the average temperature of the coldest quarter (almost the same as the driest) varies from 10.8 to 3.6 • C. The annual amount of precipitation, contrary to our expectations, does not increase when climbing the mountains and falls from 2335 to 1822 mm per year. Moreover, this change occurs mainly due to a decrease in the amount of precipitation in the warmest season. The amount of precipitation for the warmest quarter falls from 1254 to 998 mm depending on the elevation. The maximum amount of precipitation is observed in the diapason from 1500 to 1600 m a.s.l., thus not in the lowest localities. The precipitation in the driest quarter varies slightly, from 53 mm at the lowest levels to 35 mm at levels of 2000-2600 m a.s.l. m., and then slowly increasing to 39-40 mm in the apical part. Thus, the phenomenon known as the interception of moisture from moisture-bearing air masses is not observed here. At the same time, despite the decrease in the amount of precipitation toward the peaks, the vegetation of the upper belts does not have the traits of greater xerophyticity compared to the lower levels. This may be due to two factors: (1) a decrease in average temperatures at the upper levels, which also reduces the potential evaporation from the substrates and plants, and (2) frequent cloudiness in the near-top areas, which is not recorded as precipitation but significantly moistens the vegetation and reduces evaporation. One of the confirmations of this phenomenon is the wide distribution of epiphytic bryophytes, starting from 2200-2400 m a.s.l. The latter forms the appearance of communities resembling mossy forests (although not genetically related to them).

Literature Background and Specimen Collection
As is easily expected, the peculiar position and geological and topographic features of the Hoàng Liên Sơn Range have attracted the attention of many biologists, including botanists who have collected specimens on the range. The results of these studies are reflected in a number of published papers [13][14][15][16][17]. At the same time, it is worth noting that apart from our research group, only one hepatologist (Tamás Pócs) has worked on the Hoàng Liên Sơn Range. Moreover, he did not visit localities above 2000 m a.s.l. We were the first bryologists to visit the apical areas of the range (within area treated in the present account) in 2016, and since then have visited more than once. A number of new findings in the Vietnamese flora of liverworts from the Hoàng Liên Sơn Range were published earlier [4][5][6][7][8][9][10][11][12], although a total checklist of liverworts for the Hoàng Liên Sơn Range has never been published.
The territory of the park and adjacent areas, as identified in the present account, was surveyed by our group in 2016, 2017, 2018 and 2022, no more than a week each year, usually in April. A total of 1320 specimens were collected, with 2219 determinations, because specimens commonly have more than one species inside. All liverwort specimens after collection were stored in the fridge under anabiosis conditions to keep them alive and, therefore, prevent the destruction of oil bodies in the cells. In 2016, 2017 and 2018, the specimens were transported to Vladivostok to the Cryptogamic Biota Laboratory (Botanical Garden Institute, herbarium acronym VBGI) for identification; approximately 30% of these specimens were then frozen, and the "shock" nature of freezing led to the death of oil bodies in approximately 50% of the frozen material. In 2022, to avoid alive specimen death, all material was delivered to Hanoi to the Laboratory of Plant Ecology (Institute of Ecology and Biological Resources, herbarium acronym NH), where the material was identified by morphological methods. In both cases, the general appearance of plants and oil bodies was photographed for approximately 70% of the collections of 2016-2018 and 70% of the collection of 2022. Only after the end of the identification were all specimens dried. To take photographs of the collected plants, we used microscopes in the laboratories of VBGI and HN, with the most valuable ones in the Laboratory of Plant Ecology at the Institute of Ecology and Biological Resources of Vietnam Academy of Science and Technologies, including a Nikon SZM800M and Olympus BX43, both equipped with digital cameras.
The results of the identifications were later input into a database, from which an extraction was then obtained and later processed manually using PC software. Literary references were added to the obtained draft list. In most cases, it was impossible to reliably understand from old literary sources whether the distribution of the species was indicated within the park (the park was founded only in 2006) or belonged to its environs because, in the vast majority of cases, only the geographical description "Sapa" was indicated. Fortunately, in most cases, the literature provides data on the elevation above sea level of the collection locality. Presumably, all localities above 2000 m a.s.l. belong to the park, and those below 1700 are outside the park. However, the specimens collected between 1700 and 2000 m a.s.l. could be gathered both within the national park and outside it.
as the Anacardiaceae, Dipterocarpaceae, Euphorbiaceae, Meliaceae and Simaroubaceae and an increase in dominance of subtropical and temperate families like Fagaceae, Theaceae, Magnoliaceae and a diverse assemblage of conifers".
Due to elevations lower than 1300 m a.s.l. being absent in the studied area, we did not study the typical tropical forests developed in the lowlands of Northern Vietnam at elevations below 1000 m a.s.l. The typical landscapes and liverwort habitats are in Figure  5.

Flora Analysis Methods
Detrended correspondence analysis (DCA) was used to identify the trends in altitudinal formation of the studied flora and the relationships of the total taxonomic list of the studied flora with other flora lists for some adjacent areas. This multivariate statistical technique was chosen because it is suitable for finding the main factors or gradients in large, species-rich but usually sparse data matrices. DCA was performed using Past ver. 4.03c [41].
This type of analysis was applied to two issues raised.
(1) Comparison with the floras of adjacent areas. For comparison, we chose the richest local floras in the adjacent regions of Yunnan Province and the Guangxi Zhuang Autonomous Region in China. Unfortunately, there are no summarized data on local floras in Northern Thailand, and they are not in Laos, where all known diversity is limited by 66 species [18]. Thus, the comparison turned out to be rather one-sided, since it included data only on the floras of the areas adjacent to the north. A list of floras with indications of sources is given in Table 11. In addition, since the distances between the coordinates of the positions of floras in a three-dimensional system are a dimensionless (conventional) value, we made an attempt to compare the average distances at the southern tip of the East Asian region with the average distance between the additionally involved floras at the northern tip of the East Asian Floristic Region and adjacent Northeast Asia, belonging to the Circumboreal Floristic Region [2]. Unfortunately, only a small number of local floras can be considered sufficiently studied. As a result, four additional floras were chosen, two of which are located in the north of the East Asian region, and two are in the middle part of Pacific Northeast Asia. These floras were Iturup Island, Jiri-san National Park, Bystrinsky Nature Park and the Commander Islands. The information about all compared floras is placed in Table 11.
Thus, a matrix was compiled, including a cumulative list of species for all 8 floras, in which the presence of a species was indicated by the number 1 and the absence by the sign 0. This matrix is provided in the Supplementary Material (Table S2). A summary diagram was made for all floras, and conditional coordinates were determined in a three-dimensional grid obtained by DCA for each set of floras mentioned above. Next, the distances were identified in conventional units between all floras of each set. In addition, the distances in kilometers along the geodesic line between all floras of each set (based on the central point of the compared floras) were determined for subsequent comparison of the comparability of the geographical distance with the distances in the DCA matrix.
(2) To formalize the description of changes in the liverwort flora of the studied area depending on elevation, two matrices were compiled on the distribution of taxa within the altitudinal range. Both matrices are based on the list of species of the study area, and the presence of a species within the altitudinal range is marked with a 1 (absence is 0). One matrix was compiled according to the distribution of taxa within the hundred-meter ranges (1300-1399, 1400-1499 m a.s.l., etc.), while the second operated on 200-m ranges. In the first case, the diapasons are named in formats such as >1300, >1400, etc., whicih means the gaps 1300-1399, 1400-1499, etc., correspondingly. In the second case, a gap >1200 means that the diapason is 1200-1399 m a.s.l. Because the ranges were unevenly explored, and, for some, too little data were collected, before being included in the analysis, all ranges in which less than 40 species were known were removed from the analysis to exclude aberrations due to insufficient data. The following ranges were excluded: 1400-1499, 1600-1699, 1700-1799, 2300-2399, 2400-2499, 2500-2599, 3000-3099, 1600-1799 and 2400-2599 (Table S3).

Conclusions
The liverwort flora of the studied area, located in the central part of the Hoàng Liên Sơn Range, is very rich taxonomically. The data presented in this paper will undoubtedly be supplemented in future targeted research. In general, the flora possesses distinct Sino-Himalayan features, which is a typical trait of the floras in the northern tip of Indochina. At the same time, a comparison with the nearest well-studied regional floras in Southern China showed the significant differentiation of the flora of the studied region from the nearest floras adjacent to the north. The uniqueness of the studied area is determined by the close interpenetration of the Sino-Himalayan flora into the Indochinese, which, due to the significant altitudinal range of the study area, contributed to the formation of an original and very rich flora that promises numerous new records in the future.