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An Ethnobotanical Study of Indigenous Medicinal Plants of Oman



Neelam Sherwani, Khamis Sulaiman Al-Dhafri and Sardar A. Farooq
 
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ABSTRACT

Background and Objective: Sultanate of Oman abodes immense biodiversity, including some unique, threatened, endemic and regionally endemic medicinal flora confined to specialized ecological niches carved under the complex geographical terrain of this arid desert biome. In the current study, we systematically documented the diversity and therapeutic uses of medicinal plants. Materials and Methods: An intensive ethnobotanical survey carried out in different physiographic regions of the Sultanate of Oman for a time of 4 years 2014-2018. Results: A total of 437 medicinal plants are found across the geographical extent of Oman, of these 160 common medicinal plants were verified and documented for their distribution and therapeutic uses in the traditional indigenous tribes of Oman. Among these 160 medicinal species belong to 53 families and 131 genera. Fabaceae and Asteraceae were the dominant families contributing remarkably to the local ethnomedicinal tradition. Other pharmacologically active species were found among Apocynaceae, Euphorbiaceae, Lamiaceae, Amaranthaceae and Solanaceae. In general, leaves are the preferred part used to alleviate an ailment, followed by usage of the whole plant to mitigate the malady. Conclusion: This baseline survey of ethnomedicine can lead to contribution in the field of drug discovery since Omani medicinal plants are not yet fully exploited commercially for their medicinal uses, besides, at present without any in situ protected area to conserve medicinal plant diversity in Oman. This study also emphasizes the importance of setting up strategies and conservation priorities and the utilization of ethnomedicinal plants.

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Neelam Sherwani, Khamis Sulaiman Al-Dhafri and Sardar A. Farooq, 2021. An Ethnobotanical Study of Indigenous Medicinal Plants of Oman. Asian Journal of Scientific Research, 14: 43-56.

DOI: 10.3923/ajsr.2021.43.56

URL: https://scialert.net/abstract/?doi=ajsr.2021.43.56
 
Copyright: © 2021. This is an open access article distributed under the terms of the creative commons attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

INTRODUCTION

Pharmacologically active phytochemicals of ethnomedicinal plants had played a pivotal role in the primary health care system since time immemorial. The traditional herbal medicine system is universally the most extensive system of medical care with globally 70-95% of the population of developing countries relying on the traditional herbal treatment as Materia Medica for their primary health care1. Even much of the understanding of the contemporary western- allopathic medicine which is widely practiced in the developed world can be owed to plant’s active pharmacological principles since medicinal plants still represent an important reservoir for the formulation of novel drugs. Indeed, approximately a quarter of all the prescription medicines presently in use in the market have their origin from active ingredients of medicinal plants2. Around 48.6% of the anti-cancer drugs can be sourced back to plant-based natural products and in fact out of the 1562 FDA-approved drugs between the period of 1981-2014, about 38.1% are based on natural products (majority plant-based) and their derivatives3. Herbal medicine is certainly a popular and strong growing trend owing to emerging consumer concerns regarding possible side effects of many synthetic allopathic medications and recent enhanced Antimicrobial Resistance (AMR) against in the use of infectious diseases drugs. With 10 million lives estimated to be lost per year by 2050 due to AMR, there is an increased emphasis and surge in exploring medicinal plants for phytopharmaceuticals as novel antibiotics against deadly infectious diseases4.

Globally in 2016, the trade-in herbal medicine was evaluated at USD 71.19 billion5 and is expected to witness substantial growth, the Globe Newswire has projected the world trade of herbal medicine to exceed USD 411 billion by 2026 due to the surge in demand for herbal products in the healthcare system globally.

World Health Organization (WHO) as a part of its Sustainable Development Goals 2030, included Traditional and complementary medicine in specifications of essential health services and via the Declaration of Astana (Oct 2018) WHO declared to apply both scientific as well as traditional knowledge to strengthen primary health care services worldwide6. Total 170 member states have pledged to develop national-level policies and strategic plans to regulate practices and products of traditional medicine and have acknowledged the appropriate stepwise integration of traditional and complementary medicine into the health care system.

The Sultanate of Oman with an estimated land area spanning across 309,500 km2 and coast of 1,700 km is home to a vast number of unique, rare and endemic flora owing to its strategic positioning on the Northern tropic, the latitudes of Cancer, a transitional latitudinal zone between tropical and subtropical climatic belts and notably diverse geography. Marked geomorphological and geological heterogeneity, resulted in an array of exclusive ecological niches and domains of microenvironments, the habitats, varying from desert gravel plains, salt flats, lagoons, hyper-arid deserts, dunes, wadis, rugged mountain ranges and coastal plains7. These specific habitats sustain special divarication of species inducing distinct biological flora. Oman a desert geographical land form is floristically endowed with rich and diverse flora, with 1407 plant species found across the latitudinal gradients of Oman8, but as water-limited lands are well known to trigger speciation of species, Oman is home to some unique and rare flora, displaying the significant degree of endemism with 84 plant species exclusively endemic to Oman8 this flora is geographically confined, unique, ecologically meagre and many of them are threatened and endangered. In specialized dry realms, extreme xeric environmental conditions, torrid heat and water stress establish unique and distinctive habitats, where biota under the influence of local phytoclimate accrue some unique phytochemicals as an adaptive response for their survival and defense9. Owing to this Oman is a crucial emporium of some unique endemic or near-endemic medicinal plants, which are restricted to Oman and nearby regions.

Indigenous knowledge of these medicinal plants, their properties, active principles, the way of preparations and their toxic potential is available among local elder generation and medicinal healers but was rarely recorded and is rapidly depleting as it is passed down through generations only by oral tradition and has never been properly documented or commercialized on a larger scale as done in other countries globally. Given the unique and diverse nature of the medicinal flora present and the diminishing traditional therapeutics knowledge, the documentation and conservation of the important and endangered medicinal species in the wild are imperative. Few studies were done earlier in Oman but some are confined to smaller geographical regions of Oman and others discussed medicinal plants in the context of the Arabian Peninsula rather than Oman in particular. Parallel to this, human-induced biodiversity losses are substantially affecting the plant species in wild10, out of the 25,791 documented medicinal plant species at Royal Botanical Gardens (RBG), 723 (13%) are categorized as threatened11.

Further in desert biomes, under extreme environmental conditions, species are living at their physiological limits, biodiversity is often fragile and specifically more susceptible to climate change, easily affected by local human-induced habitat conversion, overgrazing, or over-harvesting12. Thus the scientific documentation of the medicinal flora with regards to its distribution and therapeutic uses are imperative in light of species extinction under influence of climate change, habitat destruction/fragmentation due to modernization/urbanization, unsustainable overgrazing and species invasiveness.

In this perspective, we systematically initiated the current research to document the diversity of medicinal species across the extensive geographical extent of Oman, to record the highest representation among Angiosperm families and to record the indigenous uses of these medicinal plants before this valuable information is lost forever.

MATERIALS AND METHODS

Study area: Sultanate of Oman can be divided into four physiographic regions, with distinct landscape features and climate. Along the northern frontier of Oman is an Al Hajar montane ecoregion, divided into Western Hajar ranges (Al Hajar al Gharbi) and the Eastern Hajar ranges (Al Hajar Ash Sharqi) and receives an average annual rainfall of 200/300. The 2nd region is the coastal plains along the foothills of the Al Hajar ranges. The third region, hyper-arid desert, the Central Oman plateau, with an annual average rainfall of 50 mm. The fourth zone, the southern province Dhofar, has a seasonal tropical microclimate receiving an annual mean rainfall of 250 mm/year.

Methodology: For the study, planned ethnobotanical surveys were carried out throughout the geographical extent of the Kingdom of Sultanate of Oman from 2014-2018 to document the ethnomedicinal data. Extensive field trips, semi-structured questioners and interviews were carried out to document the location and traditional therapeutic uses of the listed plants. The part of the plant used in traditional medicine was also recorded. Groups consulted for the questioners and interviews were village elders in the age group of 45-80 years who holds deep knowledge and understanding of the curative characteristics of the medicinal herbs, traditional healers in villages, herbal medical practitioners in villages and cities. In total 48 respondents were selected for interviews and questioners, out of which 36 were males and 12 were females. Several field trips were made to different localities. Specimens of all documented medicinal plants were collected, identified using the 4 volumes of Flora of Oman and other related literature, taxonomic books. The collected specimens were compared with voucher specimens of the herbarium at the Life Science Unit of SQU.

RESULTS

The results of the survey summarize the current ethnobotanical knowledge regarding the medicinal plants of Oman. In Oman, a high proportion of overall native flora exhibits pharmacological properties, with a total of 437 species of medicinal plants which are nearly 31% of the total floristic diversity (1407 species) documented in the country. These 437 medicinal species are distributed among 283 genera and 95 families and have been traditionally used to cure multiple ailments by local communities. In the present study, 160 common medicinal plant species belonging to 131 genera and 53 families were studied for their traditional uses. The collected, verified medicinal flora along with its traditional uses is documented in Table 1. From the results of the ethnobotanical survey, it’s quite evident that medicinal species diversity is not uniformly dispersed along the latitudinal gradients of Oman. Rather the medicinal species richness is aggregated into certain regions termed as Centre's of medicinal species richness in Oman (Fig. 1). 4 Centre's of medicinal species richness scattered along the geographical length of Oman were observed during this study. The Jabal Al Qara escarpment in Dhofar (Southern province of Oman) hosts the greatest species pool of medicinal plants in Oman (Fig. 1).

The second area of medicinal species richness was the Al Hajar al Gharbi ecoregion hosting high altitude Jabal Al Akhdar ranges in the North of Oman. The third species pool was documented from the Al Hajar Ash Sharqi range hosting Jabal Bani Jabir, Jabal Abyad and Jabal Aswad, mountain ranges. The fourth region of high medicinal plant diversity was Masirah island located on the eastern coast of the geographic landform of Oman in the Arabian sea. Central Oman which occupies 70% of the total geographical area of Oman shows less diversity of medicinal plants.

Out of the documented 53 families, Fabaceae/ Leguminosae with 15 species was the most dominant family have the maximum representation among the medicinal flora (Fig. 2).

Table 1:Medicinal plants species, local names, parts used, traditional uses in herbal remedies
Image for - An Ethnobotanical Study of Indigenous Medicinal Plants of Oman
Image for - An Ethnobotanical Study of Indigenous Medicinal Plants of Oman
Image for - An Ethnobotanical Study of Indigenous Medicinal Plants of Oman
Image for - An Ethnobotanical Study of Indigenous Medicinal Plants of Oman

Image for - An Ethnobotanical Study of Indigenous Medicinal Plants of Oman
Fig. 1:Distribution of medicinal plant flora along with the geographical extent of Oman

Image for - An Ethnobotanical Study of Indigenous Medicinal Plants of Oman
Fig. 2:Number of medicinal plant species per family

Image for - An Ethnobotanical Study of Indigenous Medicinal Plants of Oman
Fig. 3:Percentage of plant parts used in herbal medicine

Asteraceae with 12 species was the second most represented family in traditional medicine. The other families contributing substantially to the ethnomedicinal flora include Apocynaceae (11 spp.), Amaranthaceae (11 spp.), Capparaceae (8 spp.) Solanaceae (7 spp.) Euphorbiaceae (7) and Lamiaceae (6 spp.) and Boraginaceae (5 spp.) Almost 50% of ethnomedicinal diversity in the present study is contributed by the above-mentioned nine families. Brassicaceae, Burseraceae and Zygophyllaceae have 4 pharmacologically active species each. The rest of the 43 families either has a single species representation or 2-3 species per family.

All the different parts of plants, leaves, roots, bark, stems, sap, seeds, fruits and flowers are used to treat various types of diseases since antiquity. From the documented records the leaves were the most frequently used part of a plant to cure various ailments (33%) (Fig. 3). Seeds of plants are widely used by the local community to mitigate various types of illnesses (18%), followed by the usage of a whole plant for the treatment of several diseases (12%). Roots were used to cure 10% of ailments followed by fruits used in 8% cases, stems in 7%, sap in 5%, flowers in 4% and barks in 3% cases (Fig. 3).

DISCUSSION

Our results indicated that medicinal plant species have a high representation in the flora of Oman, with 437 medicinal species found in Oman. Biota found in extreme dryland ecosystems have evolved special adaptive functional features to cope up with the limited water availability and immoderate heat prevailing in such ecosystems. Such adaptive strategies under hostile environments have immense importance in terms of survival and plants overcome these ecological constraints by regulating their phytochemicals13. The accumulation of these active principles as a physiological expression of defence is greatly influenced by the adverse abiotic environment or biotic stress and imparts exceptional medicinal properties to this unique plants14. Further, as exclusive metabolites are strongly influenced by exceptional local environmental conditions, endemic medicinal flora has phenomenal uniqueness and significance15. Thus Oman being a special desert biome is home to many medicinal plants, with many endemic species, not found anywhere else in the world. In this study, 160 common medicinal plant species belonging to 131 genera and 53 families were studied for their traditional uses. Leguminosae with 15 medicinal species was the most represented family used as herbal remedies. Overall in terms of angiosperm floristic diversity, Fabaceae/Leguminosae is the most represented family in Oman and globally this family is known for its ethnopharmacological importance16,17. Out of the total 28,187 medicinal plants registered with Kew’s Medicinal Plant Names Services (MPNS), the Leguminosae family species has the largest representation with 2,334 documented plant species18. Worldwide Fabaceae members have been used as therapeutic agents eliciting antimicrobial19 anti-inflammatory16, anti-diabetic20, anticancer21 and antiulcer22 properties. The Second highest representation in terms of medicinal plants was observed in the Asteraceae family, with 12 medicinal plants, globally many species belonging to Asteraceae are sources of potential active principles used effectively to cure many ailments23 like cardiovascular24, wound healing25, anti-inflammatory properties26 diuretic effects27, indigestion28. Apocynaceae and Amaranthaceae species were also recorded to be widely used by the local community, many medicinal attributes in traditional medicine have been documented to Apocynaceae29,30 and Amaranthaceae31,32 families previously. Apocynaceae species being well endowed with cardiac glycosides, alkaloids, steroids, flavonoids and terpenoids are potent sources of medicinally active phytochemicals. Many species in Apocynaceae are sources of natural cardenolides, a type of C- steroids, the anticancerous compounds, around 109 cardenolides has been identified from Apocynaceae members33. Solanaceae species also represented widely in this study are known worldwide as sources of tropane alkaloids, hyoscyamine and scopolamine which when used in small appropriate amounts can be an important source of medication.

Medicinal flora is not evenly distributed across Oman rather medicinal species richness is confined to certain areas called Centre of Medicinal Species richness in Oman, with 4 Centre of Medicinal Species richness recognized in Oman. The Al Hajar Al gharbi mountain ecoregion in the north with an Irano-Turanian floral influence34, is botanically abundant and supports unique flora under the effect of Northeasterly winds and is home to many medicinal plants. The flora of the Hajar Al Gharbi Mountains including the Musandam peninsula is one of the richest, with 60% of the total plant diversity of Oman represented in this region. In this ecoregion, Al Jabal Al Akhdar a massive carbonate culminations forms the central part in the Saiq plateau, which is a massif of mid-Permian to mid cretaceous black carboniferous limestone, brownish dolomite and sandstone35. At the lower elevations of the culmination, Samail Ophiolite sequences from oceanic crust are emplaced36. This dark ophiolite area does not support vegetation except in the wadis, on the other hand, floral species diversity is high in the richer soils of carbonate limestone rocks. A clear altitudinal zonation with distinct plant community composition is quite evident in these mountain ranges as elevation strongly influences the species diversity. The altitudinal gradient ranges from 650-3048 m at Jabal shams, with maximum diversity found at mid-latitudes at 1100-2000 m above sea level37. Annual rainfall at lower elevations is on average 75 mm reaching approximately 350 mm at higher elevations. The average annual temperature along the altitude varies from 26-18°C, with the temperature reaching subzero at the summit in winters leading to frost events. Thus a relatively conducive temperature and rainfall events at mid altitudinal zones support a higher diversity of plants between 1100 -2000 m above sea level. This vegetation distribution is a type of sub-arid mountain zone in a desert biome. Important medicinal plant species found in this special phytogeographical region are Euryops arabicus, Sideroxylon mascatense, Olea europaea, Teucrium stocksianum, Dodonaea viscosa and Moringa peregrina. The second centre of medicinal species richness in northern Oman is the Eastern Al Hajar Ash Sharqi ranges, a part of the Al Hajar mountain ecoregion. Hajar Al Sharqi Mountains is an arid climatic zone with a mean annual precipitation of 120 mm under the effect of northeast winds and reaching the highest altitudinal elevation of 2,152 m38. Jabal Bani Jabir, Jabal Abyad, Jabal Aswad and Jabal Qahwal are the species-rich ranges supporting many medicinal plant species. As plants species are known to accumulate specific phytochemicals as a convergent adaptive strategy as they respond to stimulations of natural regional environment39. Eastern Hajar mountains host 23% of the total floristic diversity of the country. Species wise this region has a distinct flora compared to the Western Al Hajar range. Flora of eastern Al Hajar has representation similar to the semi-arid desert steppe found in central Iran’s high inner plateau. Important medicinal plant species found in this physiographic region are, Astragalus fasciculifolius, Grewia erythraea, Lycium shawii and Haplophyllum tuberculatum.

The most important medicinal species richness centre is found down south in the Dhofar province. Lying in the monsoon belt, the Dhofar region under the effect of southwest monsoon has a seasonal summer, June to September tropical climate40. Monsoon winds cause dense coastal fogs generated due to rapid cooling of the moist westerlies along the windward sea-facing elevations of the Jabal Al Qara and Jabal Al Qamar limestone massif41, providing adequate moisture, consequently creating a unique dense green seasonal cloud forest of deciduous woodlands along the escarpment and creating an extraordinary microclimate needed to sustain a rich and unique vegetation cover42 which makes this region unique refugia and the densest woodland of the Arabian peninsula. This specialized physiographic unit supports around 70% of the species represented in the country and displays a very high degree of endemism. This Somalia-Masai influenced floristic diversity43 is mainly found in Jabal Qamar (receiving maximum precipitation, annual mean rainfall of 250 mm/year), Jabal Qarah and Jabal Samhan. Jabal Qamar hosts pharmacologically active species like Aloe dhufarensis and Boswellia sacra. Jabal Qara hosts a very important medicinal plant Lavandula dhofarensis and Commiphora kua. Jabal Samhan, the highest of the three peaks of Dhofar mountains with an elevation reaching as high as 2100, lies at the peripheries of the foggy ecosystem has dry plateaus at the summit, inundated with narrow deep wadis and gorges44 supporting endemic woody medicinal species subshrubs and trees including medicinally active species of Commiphora wightii and Boswellia. All these regions are unique niches curved under the influence of specialized environmental conditions and flora established in such biomes are rare and specialized. Masirah islands the 4th centre of endemism is the largest island 19 km from the South-eastern coast of the Sultanate of Oman into the Arabian sea, the island has a rugged hilly terrain of Masirah ophiolite a part of Indian ocean crust overlaid by Cretaceous ocean sequence45, this hilly arch runs centrally from north to south with marginal coastal plains. Many medicinal species like Suaeda monoica, Suaeda moschata and Limonium axillare are found on this island

Hyper-arid Central Oman overall shows less representation in terms of angiosperm floristic diversity and also shows minimal representation to medicinal diversity. As the interplay between the topography and the environment profoundly influences the vegetation patterns46, Central Oman a hyper-arid desert of gravel and sand with two major escarpments, the Huqf escarpment/ depression as well as Jiddat Al Arkad represents physiography of extreme aridity due to average annual rainfall of less than 48 mm and extreme raging temperatures making central Oman a desolate zone47. The major realm in central Oman is a gravel and tertiary limestone plateau, Jiddat Al-Harasis around 100-150 m above sea level, with no proper drainage system, rather the plateau is incised with not so deep sandy depressions, the Haylahs, supporting merger vegetation48. The Al Huqf escarpment/depression is a barren rocky terrain made from bigger rocks from Permian to upper Cretaceous with Oceanic Crystalline Rocks reaching the surface at certain points in the escarpment, the depression has salt plugs the sabkhas at certain areas, vegetation is rather confined to gravely sandy ridges, the runnels in the huqf under the influence of occasional fogs49. On the western fringes, Jiddat al Harasis is bounded by hyper-arid uninhabited and inhospitable region Rub al Khali or Empty Quarter the biggest active sand desert found in the world (650,000 km2). This active sea of shifting sands is an extreme environment with precipitation of hardly 15-35 mm and hosting the biggest inland brackish poisonous saline sabkha quagmire ‘Umm al Samim’ or the Mother of poisons (3,000 km2)50. Under these hostile conditions, plant species diversity is very low, represented by low growing natural psammophilus plants of Saharo-arabian types. This vegetation is highly significant in terms of stabilizing the dunes substrate, as dunes are a highly dynamic system subject to ecological changes under the influence of environmental changes. Vegetation act as a windbreaker, downscaling the topsoil loss due to wind erosion and providing habitat to many dune fauna51. As under influence of abiotic factors, plant species accrue specific bioactive principles as a response strategy52, flora found in this region is unique, endemic and some are threatened and endangered.

Climate change along with other factors like habitat degradation due to urbanization/industrialization, overexploitation of resources/ overgrazing and species invasiveness, are responsible for this exceptional biodiversity loss53. According to a new report of World Economic Forum, State of Worlds plant and fungi 2020, by Royal Botanic garden Kew, 40% of the world's plants at risk of extinction, indicating that a “sixth mass extinction” is under way54. The sultanate of Oman has quite ambitious goals regarding nature conservation as is evident from Sultanate ratification and implementation of many conservation treaties like Convention on biological diversity 2011-2020, Global Strategy for Plant Conservation 2010-2020, International Treaty on Plant Genetic Resources for Food and Agriculture. Oman’s Supreme Council for Planning (SCP) has also endorsed the United Nations Sustainable Development Goals for 2030 (SDGs) in its third meeting in 2015. For the conservation of plant genetic resources, Oman has established 18 nature reserves in form of national parks and nature reserves and 4 protected rangelands but presently there are no in situ protected areas that actively conserve medicinal plant diversity in Oman. There has been overwhelming evidence that fragile vulnerable desert biomes exhibit rapid species extinction, also regions that exhibit high topographical heterogeneity, usually experience strong climatic oscillations55. Furthermore, according to the Global Climate Risk Index 2018, Oman has ranked 28th in terms of climatic risk, in this regard it is imperative to document and conserve the valuable medicinal flora of a fragile desert ecosystem like Oman. Traditional knowledge of a particular culture is a heritage accumulated from centuries of practices that need to be valued and conserved. Further, the emerging and the ongoing trend of herbal products derived medicine has enormous potential to directly or indirectly benefit economically the current and coming generations.

CONCLUSION

Oman has a rich ethnobotanical traditional history and this rich culture reflects the close association of its people with plants. Our findings signified and documented the current status of the medicinal species population, their therapeutic uses, potential threats and their conservation status. This study emphasizes the prioritization of efforts to sustainably conserve the medicinal flora of this unique biome, efforts should be made to identify, extract and isolate the pharmacologically active principles, establish their physiological effects and analyse their cytotoxic potential before this indigenous valuable heritage is lost in the process of modernization of the society. There is an imperative need for in-country commercialization of medicinal plants and impetus should be given to establishing pharmaceutical companies using local Omani medicinal plants.

SIGNIFICANCE STATEMENT

In the light of the unprecedented loss of biodiversity under the impact of ongoing climatic change crisis and the traditional herbal medicine knowledge being mainly undocumented, this study is a keystone work in direction of harnessing the untapped potential of local Omani medicinal plants to discover new bioactive principles for drug discovery which will financially benefit the local community at a larger scale as the local medicinal flora of Oman which shows high degree endemism is unexplored commercially.

ACKNOWLEDGMENTS

The authors would sincerely acknowledge and appreciate the valuable knowledge the local elders and herbal practitioners have shared, our gratitude towards their kindness and our appreciate and recognize their contribution to this study. We also like to thank the team at Herbarium, Life Science unit, SQU for their help.

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