Analysis of floristic composition and species diversity of vascular plants native to the State of Palestine (West Bank and Gaza Strip)

Abstract This study aims at providing an updated checklist of the native vascular flora of the Palestinian West Bank and Gaza Strip (State of Palestine, SP), serving as a taxonomic and nomenclatural basis for botanical research and encouraging new floristic surveys and biosystematic studies. The study provides an up-to-date checklist of native vascular taxa of the SP and their distribution within the plant districts in the country. This is the very first annotated checklist for the native vascular plants of the SP which incorporates recent name changes, new distribution records, habitat, herbarium specimens catalouge, Red List criteria, wild edible plants, endemism and use in Traditional Palestinian Herbal Medicine. The quantitative analysis of the flora has shown that the SP hosts 1826 taxa, distributed in 686 genera and 108 families; five taxa are gymnosperms, nine taxa are Pteridophytes and 1812 taxa are angiosperms. The most represented families are Leguminosae (222 taxa, 12.2%), Asteraceae (197, 10.2%) and Poaceae (196, 10.7%), while the most represented genera are Trifolium (38, Leguminosae), Silene (32, Caryophyllaceae), Astragalus (27, Leguminosae), Medicago (26, Leguminosae), Allium (25, Amaryllidaceae) and Euphorbia (25, Euphorbiaceae). Annuals (52.4%), Hemicryptophytes (20.2%) and Chamaephytes (12.2%) are the most represented life-forms amongst the SP flora. The richest plant districts in the SP vascular plant taxa are Gaza Strip (GS) (1216 taxa), Jerusalem and Hebron Mountains (JHM) (1235) and Nablus Mountains (NM) (1126). Agglomerative hierarchical clustering (AHC) permitted the division of SP into two main regions, based on the existence of vascular plant taxa: Region 1 (western plant districts with 1128-1237 taxa) with higher water availability and temperate Mediterranean climate which permit the establishment of more than 65% of the total SP flora in these districts and Region 2 (eastern plant districts with 571-698 taxa), characterised by desert and semi-desert conditions, as well as the presence of alluvial and co-alluvial soils, which allow the survival of lower numbers of plant taxa. One hundred and sixty-five taxa of the SP flora are endemic and near-endemic. However, in comparison with some countries of the Mediterranean Basin, this number is below the average endemism concentration, along with other southern arid countries, such as Tunisia and Egypt. In total, there are 102 threatened plant taxa, belonging to 39 families and 83 genera representing 5.6% of the total plants in the SP. IUCN and the Conservation Measures Partnership (CMP) unified classification of direct threats for SP Red-Listed plants has shown a high extinction risk to the Palestinian threatened wild flora, with 76.5% of the threatened species being either critically endangered (CR) or endangered (EN); only 23.5% were vulnerable (VU). However, several taxa are threatened by numerous factors including small population size, human activities, for example, conversion of traditional to intensive agriculture accompanied by deep ploughing and the application of pesticides, urban development and construction, global climatic change, drying of marshes and wetlands, quarrying, fires and pollution. This checklist can help focus conservation efforts and provide a framework for research, protection and policy applications for the SP flora, especially for the endemic and threatened plants.


Introduction
The flora of the State of Palestine, SP (West Bank and Gaza Strip) has been partly covered by several authorities including Flora Palaestina (Post 1932, Post 1933, Zohary 1966, Zohary 1972, Danin 1988, Feinbrun-Dothan and Danin 1991, Danin 1992, Sapir et al. 2003, Danin 2004, Shmida and Pollak 2007, Horvitz and Danin 2015. Far fewer studies have dealt with the flora of the SP (Ali-Shtayeh and Jamous 2018). The latter study provided a preliminary checklist of vascular plants of the West Bank and Gaza Strip (State of Palestine, SP). The checklist has shown that the vascular flora of the SP comprises 1938 taxa in 733 genera and 111 families. The checklist, however, presented few taxonomic, morphological, chorological and ecological data on each plant in the list, including life form, chorotype and pollination type. It also included 79 introduced taxa, 18 extinct, 10 with mistaken distribution and eight synonyms. In addition, no herbarium specimens were cited for the taxa included, nor was a quantitative floristic analysis provided.
On the other hand, the Red-Listing of threatened vascular plant taxa has received special attention Jamous 2002, Ali-Shtayeh andJamous 2018). Such a Red List can help focus conservation efforts and provide a framework for research, conservation and policy applications for the SP flora, especially the endemic and threatened plants. The 2018 Plant Red list of the SP flora comprises 102 taxa and suggested conservation recommendations for threatened plants. The threatened vascular plant species (102 taxa) listed in the Red List were assessed on the basis of taxonomy, distribution, population size and trends, habitats and ecology and threats, in accordance with IUCN Red List Categories and Criteria, Version 3.1. The "red number" method (Sapir et al. 2003) with some modifications (Ali-Shtayeh and Jamous 2018) was used, as complementary to IUCN Criteria, to calculate the red numbers for the plants in order to identify the threshold for the endangered status of a plant species and rank the degree of risk. The modified "rednumber" method uses six quantitative criteria (rarity, habitat vulnerability, attractiveness, distribution type (endemism), disjunctiveness and peripherality) which are combined into a single quantitative index known as the "red number". Each criterion has its own scale, which reflects its relative weight in determining the extent to which a certain plant species is endangered.
A couple of local studies "reported" a preliminary checklist of 1612 plants of the West Bank (Al-Sheikh et al. 2000, Al-Sheikh 2019, Al-Sheikh and Qumsiyeh 2021) and a third one published a preliminary checklist of 600 rare plants in the area (Al-Sheikh and Qumsiyeh 2021). However, the three studies were found to be flawed and all share the following characteristics: (a) the methods used to identify species are either not reported or are inappropriate, (b) the study methods are not described in sufficient detail or clarity to enable the reader to repeat them, (c) the statistical methods used in the research are either not suitable and/or the assumptions on which they are based do not fit the data that were used to analyse and (d) the results and conclusions are unclear, incorrect, meaningless or incomprehensible (Altman and Moher 2014, Buxton et al. 2021, Ford et al. 2021, Peres et al. 2021).
In the present study, we examine plant diversity in the SP and explore the potential influence of variation in plant districts and habitats on such diversity. We undertook the IUCN-CMP Unified Classification of Direct Threats (Version 3.2) and Conservation Actions Needed (Version 2.0) to the threatened plant species affected by the first level of threat types in order to determine the main causes threatening the existence of the plant and conservation priorities or human-activity-related extinction probability.
Our aims were: (1) to update the checklist of the SP native vascular plants flora. The update combines published and unpublished lists and survey reports to include all names that have been used and are in use for the flora of SP, with additional information on taxonomy, morphology, ecology and herbarium specimens cited for the taxa included; (2) to describe species distributions over the whole region and locate areas of highest interest for plant diversity; (3) to evaluate the influence of plant district, location and habitat on the floristic diversity of sites; (4) to identify the main causes threatening the existence of the plant and conservation priorities or human-activity-related extinction probability.

Study area and current vegetation status
The State of Palestine (West Bank and Gaza) (SP) is located within historic Palestine, with a total area of 6257 km . The geographical location of SP is between 31°13' and 32°33' Latitude and between 34°13' and 35°34' Longitude. In spite of its small area, SP is categorised by a pronounced variation in topography and climate. Five topographical zones can be distinguished in SP, including the Central Highlands, Semi-Coastal Region, Eastern Slopes, Jordan Rift Valley and Coastal Region (Ali-shtayeh et al. 2003). The SP can be divided into two climatic regions: the Eu-Mediterranean climate, which includes the coastal plain, the mountain range and the central hills. It is characterised by a mild rainy winter that lasts about six months and a warm, dry summer, with a rainfall rate ranging between 350-1000 mm; and the Xero-tropical climate zone, which includes the Jordan Valley, is characterised by warm winter and extremely hot dry summer and a lack of rainfall. These conditions are considered insufficient to support continuous plant life (Shtayeh and Hamad 1995).
The average annual temperature in the Mediterranean climate zone ranges between 17 and19°C and its average in the hottest months of August is between 22 and26°C and in the coldest months of January between 8 and10°C. The temperature may rise to 40°C in summer and fall to -6°C in winter. In the Jordan Valley, the average annual temperature ranges between 21 and25°C and its average in the hottest months (August) ranges between 21 and32°C and in the coldest months of January between 4 and6°C. The temperature may reach 48°C in summer and drop to -2°C in winter.
The SP can also be divided into four phytogeographical regions including the Mediterranean, the Irano-Turanian, the Saharo-Arabian and the Sudanese Penetration regions (Zohary 1972, Fienburn-Dothan 1978, Fienburn-Dothan 1986. Despite the small area of the SP, this confluence of the four regions has led to the rich diversity in plant communities and their components.

Specimen collection and identification
Between November 2011 and May 2020, the research team consisting of botanists from the Biodiversity and Environmental Research Center (BERC) carried out several explorations (surveys) in the SP. A combination of standard sampling methods for plant specimen collection and sight observation was used to aid the characterisation of the  vegetation (Danin 1988, Al-Eisawi andOran 2015). Specimen details included life form, habitat, distribution and collector details. The specimens were then preserved by pressing. Voucher specimens were deposited at BERC Herbarium, Til, Nablus, SP, labelled with the plant's scientific name and common names, collection date, GPS coordinates, habitat, collector, identifier and a herbarium specimen number.  Near-endemic and endemic plant diversity within the vascular flora of the State of Palestine.
Plant families with the highest representations of the Palestinian flora.  Table 5.
Habitat preferences of Palestinian plant taxa. The current checklist is an additional update, combining published and unpublished lists and survey reports to include all names that have been used and are in use for the flora of SP, with additional information on taxonomy, morphology, ecology and herbarium specimens cited for the taxa included. However, the taxa which are introduced (79), extinct (18), with mistaken distribution (10) and synonyms (8)

Data analysis
A data matrix of 1826 taxa and seven plant geographical districts was developed and agglomerative hierarchical clustering (AHC) was carried out using SPSS V21 to construct homogeneous classes of floristic districts on the basis of their Jaccard dissimilarity in the composition of plant taxa (Roleček et al. 2009).
Analysis of floristic composition and species diversity of threatened plants (102 species) and the classification of direct threats to these species were based on the updated 2018 Red Plant List of the SP (Ali-Shtayeh and Jamous 2018). In the latter study, the threatened vascular plant species were assessed on the basis of taxonomy, distribution, population size and trends, habitats and ecology and threats, in accordance with IUCN Red List Categories and Criteria, Version 3.1. The "red number" method (Sapir et al. 2003) with some modifications was used, as complementary to IUCN Criteria, to calculate the red numbers for the plants in order to identify the threshold for the endangered status of a plant species and rank the degree of risk. The modified "red-number" method uses six quantitative criteria including rarity, habitat vulnerability, attractiveness and distribution type (endemism), which are combined into a single quantitative index known as the "red number". Each criterion has its own scale, which reflects its relative weight in determining the extent to which a certain plant species is endangered.

Unified Classifications of Threats and Conservation Actions
To determine the main causes threatening the existence of the plant and conservation priorities or human-activity-related extinction probability, we applied the IUCN -Conservation Measures Partnership (IUCN-CMP) Unified Classification of Direct Threats (Version 3.2) ( Table 8) and Conservation Actions Needed (Version 2.0) to the percentage of the 102 threatened plant species affected by the first level of threat types (156 total threats; threat data were from Ali-Shtayeh and Jamous (2018)) (IUCN 2019); the results are presented in Table 8 and Fig. 12. The application of these classifications offers an indication as to the main causes threatening the existence of the plants. It also helps determine conservation priorities or human-activity-related extinction probability and is expected to help practitioners more systematically identify threats and appropriate actions.   According to our results, SP hosts 1826 plant taxa. This is in partial disagreement with our previous checklist (Ali-Shtayeh and Jamous (2018); 1938 taxa). The reduced number of total flora in SP is mainly due to the exclusion of introduced (79) and extinct taxa (18) from the current checklist. Additionally, five taxa were excluded because they were synonymised with other taxa. In addition, 10 taxa were excluded due to recent updates in their geographical distribution.

Level of Classification
As this checklist is also present in an electronic format, it is relatively easy to keep the plants of SP up to date and we hope that it will form the basis of a national flora of SP.

Diversity within the native vascular flora of the Palestinian West Bank and Gaza Strip
The native vascular flora of the SP comprises 1826 taxa in 686 genera belonging to 108 families of flowering plants (Suppl. material 1). The Pteridophytes are represented by three families, six genera and nine taxa. The Gymnosperms are represented by three families, three genera and four taxa. The angiosperms consist of 1813 species grouped in 102 families and 677 genera. The top 10 species-rich families are shown in (Table 3) (Table 4).

Distribution of Palestinian flora
The plant species richness in absolute numbers is not uniformly distributed across the plant districts; as a general pattern, GS (1216 taxa), JHM (1235) and NM (1127) are richer in absolute numbers of native vascular plants than other districts (Fig. 3).
The AHC analysis divided the SP into two principal regions according to the presence of plants; cluster 1 includes the western plant districts JHM, NM and GS characterised by high rainfall as well as mountainous, hilly, semi-coastal and coastal topography with mainly Terra rossa and alluvial soils; and cluster 2 includes the eastern plant districts JHW, NW, DSV and LJV characterised by desert and semi-desert conditions, as well as the alluvial and coalluvial soils (Fig. 5). The limited availability of water in arid and semi-arid eastern plant districts (cluster 2) allows the survival of lower numbers of plant taxa (571-698 taxa) compared with the western plant districts (1128-1237 taxa, cluster 1) with higher water availability and temperate Mediterranean climate which permit the establishment of more than 65% of the total SP flora in these districts.

Habitat preferences of Palestinian plant taxa
Our evaluation of the habitat preferences of plant taxa (Table 5) in the SP has revealed that the most common are plants of batha habitat (41.5%), followed by plants of the desert (15.9%) and humid (11.6%) habitats. On the other hand, the least common are plants of walls (0.1%), Mediterranean grasslands (0.3%) and shady rocks (0.5%) habitats.

Chorotype
Species in the plant list are categorised on the basis of their distribution type (chorotype) ( Table 7). Each plant is grouped according to its main chorotype. About 59.9% of the species in the plant list are Mediterranean, 12.0% are Irano-Turanian and 11.8% are Saharo-Arabian.

Climatic regions
An analysis of the distribution of the flora in the different ecogeographic regions shows the Mediterranean climatic region of the SP to be the most species-rich (1342 spp, 73.5%), followed by the semi-and extreme desert (844 spp, 46%) and transition zone climatic regions (735 spp, 40.3%) (Fig. 6).

Pollination system
The main pollination system in the Palestinian flora is "Animals". Of the plant list, 1424 (78.0%) of the species are animal pollinated, while 378 (20.7%) are wind-pollinated.

Endemic plant diversity within the vascular flora of SP
One hundred and sixty-five plant species (9.0% of the total Palestinian flora) are nearendemic to the SP and one or more of the neighbouring countries (Israel, Jordan, Syria, Lebanon and Egypt  (Fig. 7). However, in comparison with some countries of the Mediterranean Basin, this number is below the average endemism concentration, along with other southern arid countries, such as Tunisia and Egypt (Rankou et al. 2013, Fois et al. 2017, Abdeaal et al. 2018).

Distribution of Palestinian near-endemic flora
All plant districts in SP harbour at least one near-endemic taxon, the most near-endemic rich region is NM with 102 near-endemic taxa; followed by JHM and GS with 99 and 88 near-endemic taxa, respectively (Fig. 9).
Nine endemic taxa occur in all of the SP plant districts, forty-three taxa are endemics whose occurrence is confined to just a single region and forty endemic taxa are recorded only in two plant districts (Fig. 10).

Habitat preferences of Palestinian near-endemic plant taxa
Our evaluation on the habitat preferences of endemic plant taxa (Table 5) in the State of Palestine has revealed that the most common are endemic plants of batha habitat (45%), followed by plants of sand with 18.7%, desert and shrub steppes (12.7%). On the other hand, the least common are near-endemic plants of Mediterranean strand, ruderal and nutrient-rich soils (1%).

Distribution of life forms in the Palestinian near-endemic plant taxa
Similar to that in the Palestinian flora, the majority of endemic plant taxa are mainly annuals at 50%, followed by hemicryptophytes at 21.8% (Table 6). Herbaceous plants constitute most of the endemic flora (90.4%), followed by woody plants (16.3%).

Threatened plants
In total, there are 102 threatened plant taxa (Ali-Shtayeh and Jamous 2018), belonging to 39 families and 83 genera representing 5.6% of the total plants in the SP.
This study also shows a high extinction risk to the Palestinian threatened wild flora, with 76.5% of the threatened species being either critically endangered (CR) (39.2%) or endangered (EN) (37.3%); only 23.5% were vulnerable (VU) (Fig. 11).
The application of the IUCN-CMP Unified Classification of Direct Threats (Version 3.2) to the percentage of 102 threatened plant species affected by the first level of threat types (156 total threats; threat data were from Ali-Shtayeh and Jamous (2018) (IUCN 2019), has offered an indication as to the main causes threatening the existence of the plants (Table 8 and Fig. 12). These include: Small population size, human activities, for example, conversion of traditional to intensive agriculture accompanied by deep ploughing and the application of pesticides, overexploitation (e.g. overgrazing), urban development and construction, global climatic change, drying of marshes and wetlands, quarrying, fires and pollution (Fig. 12). The application of these classifications offers an indication as to the main causes threatening the existence of the plants. It also helps determine conservation priorities or human-activity-related extinction probability and is expected to help practitioners more systematically identify threats and appropriate actions.

Distribution of SP threatened plants
All plant districts in the SP harbour at least fifteen of the threatened taxa. The richest areas with threatened plants include JHM with 51 threatened taxa; followed by NM and GS with 44 and 33 threatened taxa, respectively (Fig. 13).
One threatened taxon occurs in all, six or five of the SP plant districts (Fig. 8). On the other hand, thirty-eight threatened taxa are confined to just a single region and thirty-five taxa were recorded in only two plant districts.
The most widespread threatened taxa are Euphorbia peplus L., Teucrium parviflorum Schreb. and Silene papillosa Boiss., which occur in at least five SP plant districts.

Habitat preferences of SP threatened plant taxa
Our evaluation on the habitat preferences of endemic plant taxa in the SP has revealed that the most common are threatened plants of batha habitat (44.1%), followed by plants of the desert with 20.6%, desert, humid habitats (11.8%) and shrub steppes and salty habitats (7.8%) ( Table 5). On the other hand, the least common threatened plants are those of the Mediterranean maquis and forest and shady rocks habitats (1%).

Distribution of life forms in the threatened SP flora
Comparable to that in the Palestinian flora, most of the threatened plants in the Palestinian flora are annuals at 39.2%, followed by hemicryptophytes at 25.5% (Table 6) and are mainly herbaceous (48%) followed by woody plants (41%).

Chorotype (distribution type) of threatened plants
Threatened plants are categorised on the basis of their distribution type (chorotype). A total of 48.0% of the species in the Red List are Mediterranean species (Table 7), but this proportion is less than that expected according to the Mediterranean chorotype proportion in the SP flora (59.9%). The Irano-Turanin species (27.5%), which grow mainly in oases along the Dead Sea Valley are also over-represented in the list (12.0%), may be due to the presence of water springs along the rift-valley, where those species grow.