Ethnopharmacology, Phytochemistry, and Global Distribution of Mangroves―A Comprehensive Review

Mangroves are ecologically important plants in marine habitats that occupy the coastlines of many countries. In addition to their key ecological importance, various parts of mangroves are widely used in folklore medicine and claimed to effectively manage a panoply of human pathologies. To date, no comprehensive attempt has been made to compile and critically analyze the published literature in light of its ethnopharmacological uses. This review aims to provide a comprehensive account of the morphological characteristics, ethnobotany, global distribution, taxonomy, ethnopharmacology, phytochemical profiles, and pharmacological activities of traditionally used mangroves. Out of 84 mangrove species, only 27 species were found to be traditionally used, however not all of them are pharmacologically validated. The most common pharmacological activities reported were antioxidant, antimicrobial, and antidiabetic properties. Mangroves traditionally reported against ulcers have not been extensively validated for possible pharmacological properties. Terpenoids, tannins, steroids, alkaloids, flavonoids, and saponins were the main classes of phytochemicals isolated from mangroves. Given that mangroves have huge potential for a wide array of medicinal products and drug discovery to prevent and treat many diseases, there is a dire need for careful investigations substantiated with accurate scientific and clinical evidence to ensure safety and efficient use of these plants and validate their pharmacological properties and toxicity.


Introduction
Medicinal plants are potential pharmacies grown in the wild and have been co-existed and co-evolved alongside human civilizations since the beginning of life on Earth. Since ancient times, human life has been revolving around plants as they were used for their curative nature to alleviate human pain and have been the focal point of many researchers since the dawn of medicine. For centuries, medicinal plants have been used as remedies for human ailments and diseases because they contain Seven types of mangrove trees exist, among which three are most dominant namely the red, black, and white mangroves. In Mauritius, two dominant types of mangrove are grown along the coastlines, namely the red (R. mucronata) and the black (B. gymnorhiza) types. Besides these two species, there is another mangrove species namely the Cassipourea gummiflua var. verticillata (N. E. Br.) J. Lewis which is scarcely cultivated in the Sir Seewoosagur Ramgoolam (SSR) Botanical Garden, Pamplemousses, Mauritius. The difference between the three most common types of mangrove (red, black, and white mangroves) is distinctive from each other based on their leaves, roots, and fruits (propagules) (http://www.mangrovesgy.org/home/index.php/2014-04-27-16-39-08/types-ofmangroves). Table 2 describes the distinguishing characteristics between the three dominant mangrove types. However, most works of literatures have not specified or classified the mangrove species on which studies were conducted concerning their types which consequently results in only a few examples given in Table 2   Seven types of mangrove trees exist, among which three are most dominant namely the red, black, and white mangroves. In Mauritius, two dominant types of mangrove are grown along the coastlines, namely the red (R. mucronata) and the black (B. gymnorhiza) types. Besides these two species, there is another mangrove species namely the Cassipourea gummiflua var. verticillata (N. E. Br.) J. Lewis which is scarcely cultivated in the Sir Seewoosagur Ramgoolam (SSR) Botanical Garden, Pamplemousses, Mauritius. The difference between the three most common types of mangrove (red, black, and white mangroves) is distinctive from each other based on their leaves, roots, and fruits (propagules) (http://www.mangrovesgy.org/home/index.php/2014-04-27-16-39-08/types-of-mangroves). Table 2 describes the distinguishing characteristics between the three dominant mangrove types. However, most works of literatures have not specified or classified the mangrove species on which studies were conducted concerning their types which consequently results in only a few examples given in Table 2 and Figure 1.
Additionally, the difference is based on the tide level they survive. For instance, red mangroves grow in the low tide, black mangroves are mostly found growing in medium high tide, while white mangroves grow on a higher tide level experiencing lower tide flushing compared to the other two types (https://wetlandsandwildlife.wordpress.com/2017/03/06/featured-content-2/). Furthermore, there are other types of mangroves known as the Buttonwood, but they are not considered as true mangroves since they produce seeds instead of propagules and grow on a higher upland area compared to white mangroves (https://wetlandsandwildlife.wordpress.com/2017/03/06/featured-content-2/).

Biogeographical Distribution of Mangroves
Mangrove forests are known as the world's most productive ecosystems, and they occur mainly in the tropical or sub-tropical regions [36]. Mangroves are found in 123 countries across the globe [14]. The total area covered by mangrove trees in the world was estimated to be 137,760 km 2 in 2000 [37] and currently mangroves covered about 152,000 km 2 [9]. Approximately 75% of mangroves are found in 15 countries with only 6.9% of them are protected [38]. The top 20 mangrove nations in the world with Indonesia covering the largest area followed by Brazil, Malaysia, and lastly Cameroon [8] are shown in Table 3. Overall, Asia consists of the largest amount of mangrove's forest (42%) in the world followed by Africa (21%), North/Central America (15%), and lastly by South America (11%).
In Mauritius, R. mucronata occupies an approximate area of 20 km 2 of the coastline of Mauritius and are found mostly on the northeast, east, and southeast coastline of the island (Grand Gaube, Pointe des lascars, Poste la Fayette, Ile aux Cerfs, Trou D'eau Douce, Beau Champ, Grand Sable, Mahébourg) and is found scarcely in the south-southwest coasts (Maconde, Tamarin) [39]. There are only two predominant species of mangroves on the island namely, R. mucronata ( Figure 2) and B. gymnorhiza ( Figure 3) [40].  Mauritius has lost 30% of its mangrove population in seven years (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994) from 20 km 2 to 14 km 2 . Mangroves were abundantly used for firewood, construction purposes, and cut to provide a pathway for boats. In the mid-1990's, a restoration program was set up and is still active. As a result, over the past 15 years, 23 hectares of mangrove trees were restored along with approximately 230,000 seedlings [41].

Morphological Characteristics
The distinct morphological characteristic of mangrove plant is linked with its root systems. All mangroves have special roots known as rhizophores (buttress, stilt, or arc-shaped prop roots) or  Mauritius has lost 30% of its mangrove population in seven years (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)) from 20 km 2 to 14 km 2 . Mangroves were abundantly used for firewood, construction purposes, and cut to provide a pathway for boats. In the mid-1990's, a restoration program was set up and is still active. As a result, over the past 15 years, 23 hectares of mangrove trees were restored along with approximately 230,000 seedlings [41].

Morphological Characteristics
The distinct morphological characteristic of mangrove plant is linked with its root systems. All mangroves have special roots known as rhizophores (buttress, stilt, or arc-shaped prop roots) or Mauritius has lost 30% of its mangrove population in seven years (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994) from 20 km 2 to 14 km 2 . Mangroves were abundantly used for firewood, construction purposes, and cut to provide a pathway for boats. In the mid-1990's, a restoration program was set up and is still active. As a result, over the past 15 years, 23 hectares of mangrove trees were restored along with approximately 230,000 seedlings [41].

Morphological Characteristics
The distinct morphological characteristic of mangrove plant is linked with its root systems. All mangroves have special roots known as rhizophores (buttress, stilt, or arc-shaped prop roots) or pneumatophores (pencil-like roots). These types of roots act as a respiratory system for the plants to facilitate gas exchange since mangroves grow in high saline conditions and anaerobic soils. Mangroves are called halophytes since they have good salt tolerance and filter sea water effectively for their usage. The height of the plants varies from 2 m to 50 m. Their leaves are thick, elliptical in shape, and dark green in color, except for Nypa fruticans Wurmb (commonly known as Nypa palm) species which have thin long leaves resembling leaves of a palm tree. The fruits of most mangrove species have a cigar-shaped structure (long and cylindrical), green in color, and varying in length ranging from 2 cm to 25 cm. Table 4 summarizes the morphological characteristics of various mangrove species.

Ethnopharmacological Uses
Mangroves have shown potential and promising therapeutic applications to treat a variety of ailments as reported by many ethnomedicinal studies. Various parts of the plants such as the leaves, roots, barks, or stems have been used in folk medicines. They are mainly used medicinally to treat diabetes, hypertension, and gastrointestinal disorders such as constipation, diarrhea, dysentery, dyspepsia, hematuria, and stomach pain. The plants are mostly used in Asian countries, namely India (45.8%), Bangladesh (5.1%), Malaysia (5.1%), China (5.1%), Indonesia (3.4%), Philippines (3.4%), and other countries with 16.9%. (Figure 4). No report is available for the traditional usage of mangroves in European countries.

Ethnopharmacological Uses
Mangroves have shown potential and promising therapeutic applications to treat a variety of ailments as reported by many ethnomedicinal studies. Various parts of the plants such as the leaves, roots, barks, or stems have been used in folk medicines. They are mainly used medicinally to treat diabetes, hypertension, and gastrointestinal disorders such as constipation, diarrhea, dysentery, dyspepsia, hematuria, and stomach pain. The plants are mostly used in Asian countries, namely India (45.8%), Bangladesh (5.1%), Malaysia (5.1%), China (5.1%), Indonesia (3.4%), Philippines (3.4%), and other countries with 16.9%. (Figure 4). No report is available for the traditional usage of mangroves in European countries. Species such as B. gymnorhiza (17%), R. mucronata (14%), A. ilicifolius (10%), and H. fomes (9%) are widely used traditionally and possess an array of potential medicinal values compared to the other species (Table 5 and Figure 5). For instance, A. ilicifolius is used to treat asthma, diabetes, hepatitis, leprosy, rheumatism, snake bites, among others. In India, the fruits are crushed and used as a dressing for snake bites. Additionally, the whole plant can be boiled in water, and the resulting decoction can be consumed to remove kidney stones [58]. In India, the bark decoction of X. granatum, although poorly exploited (1.85%), is used for treating cholera and diarrhea [58].    Species such as B. gymnorhiza (17%), R. mucronata (14%), A. ilicifolius (10%), and H. fomes (9%) are widely used traditionally and possess an array of potential medicinal values compared to the other species (Table 5 and Figure 5). For instance, A. ilicifolius is used to treat asthma, diabetes, hepatitis, leprosy, rheumatism, snake bites, among others. In India, the fruits are crushed and used as a dressing for snake bites. Additionally, the whole plant can be boiled in water, and the resulting decoction can be consumed to remove kidney stones [58]. In India, the bark decoction of X. granatum, although poorly exploited (1.85%), is used for treating cholera and diarrhea [58].

Ethnopharmacological Uses
Mangroves have shown potential and promising therapeutic applications to treat a variety of ailments as reported by many ethnomedicinal studies. Various parts of the plants such as the leaves, roots, barks, or stems have been used in folk medicines. They are mainly used medicinally to treat diabetes, hypertension, and gastrointestinal disorders such as constipation, diarrhea, dysentery, dyspepsia, hematuria, and stomach pain. The plants are mostly used in Asian countries, namely India (45.8%), Bangladesh (5.1%), Malaysia (5.1%), China (5.1%), Indonesia (3.4%), Philippines (3.4%), and other countries with 16.9%. (Figure 4). No report is available for the traditional usage of mangroves in European countries. Species such as B. gymnorhiza (17%), R. mucronata (14%), A. ilicifolius (10%), and H. fomes (9%) are widely used traditionally and possess an array of potential medicinal values compared to the other species (Table 5 and Figure 5). For instance, A. ilicifolius is used to treat asthma, diabetes, hepatitis, leprosy, rheumatism, snake bites, among others. In India, the fruits are crushed and used as a dressing for snake bites. Additionally, the whole plant can be boiled in water, and the resulting decoction can be consumed to remove kidney stones [58]. In India, the bark decoction of X. granatum, although poorly exploited (1.85%), is used for treating cholera and diarrhea [58].    B. gymnorhiza (Rhizophoraceae) is widely distributed in the Indian Ocean through Malaysia and Australia. The leaves and roots are mostly used in Bangladesh, China, India, and Indonesia to treat angina, diarrhea, eye disease, fever, hypertension, and intestinal worms, among others. In Comoros and Mauritius Islands, a decoction prepared from the root (15 cm length) of B. gymnorhiza and five to seven leaves of Piper borbonense boiled in two cups of water, is taken twice in a day to treat haemorrhage [13]. The same decoction is also used for diabetes and hypertension.
R. mucronata (Rhizophoraceae) is commonly found in East Africa, Australia, and the Indian Ocean. R. mucronata is widely used in India. This mangrove species has tannins up to 70% of tannins which is responsible for the medicinal properties including astringent, anti-diabetic, anti-rheumatism, and hypotensive [13]. The plant is most traditionally used against diarrhea, constipation, nausea, hematuria, and diabetes. In New Guinea, it is used to cure fertility and menstruation disorders [59]. Interestingly, in Indonesia, the whole plant is used to treat elephantiasis, which is a condition caused by the enlargement of tissues due to filarial worms [60,61]. Both Bruguiera and Rhizophora genera are known to be useful for treating a wide array of diseases such as angina, haemorrhage, hematuria, and interestingly, mature leaves and roots can be used for childbirth [62], ulcers [63], diarrhea, fever, burns [64], and stings of poisonous fish [13]. Table 5 summarizes and gives a greater insight into the traditional uses of different mangrove species in different countries.

Pharmacological Activities
The importance of mangroves in the medical field for curing diseases cannot be undermined as the plants have much therapeutic potential. Mangroves were used in folklore medicines a long time ago, and different extracts from various parts of the plants (roots, leaves, fruits, bark, and resin) have shown exciting and significant inhibitory activities in many assays namely antidiabetic, anti-inflammatory, anti-cancer, anti-ulcer, anti-tumor, anti-viral, antioxidant, and antimicrobial among others. Since various parts of the plants were used for inhibitory assays and considering the fact that mangrove ecosystems are known to be threatened, it can be said that plant samples were being used sustainably. Although many mangrove species have been used traditionally by local inhabitants for an extended period following folk traditions in various countries as ailments, many among them have not been studied extensively yet, and thus their medicinal properties have not been reported. For example, in Mauritius, local people use the root decoction of R. mucronata against diabetes, but the plant has not been locally validated by researchers to confirm its pharmacological properties. Similarly, no scientific research has been carried out so far on Ceriops tagal and Kandelia rheedii to prove their efficacy against diseases that can be cured by folk medicine. Interestingly, although few studies have been conducted on the species Bruguiera sexangula, Rhizophora stylosa, and Pelliciera rhizophorae, these species are yet to be used in folk medicine (Table 6). Therefore, mangrove species require more attention from researchers to shed more light into the traditional and pharmacological uses of these unique plants as there is a dearth of knowledge on this particular area. Table 6 shows the number of species used in folklore medicines and those that are pharmacologically tested. It has been acknowledged that out of the 84 mangrove species that exist, only 26 species were mentioned in literature to possess folklore medicinal importance. However, it could be possible that the remaining 58 species have an equally influential role in the management of diseases, but due to a lack of interest, there is a dearth of knowledge of all the mangrove species. Table 7 represents the pharmacological activities of various mangrove species studied and gives a broader knowledge on the pharmacological importance on mangroves and on the different types of assays conducted. Figure 6 illustrates the types of extracts commonly used for these assays.
Methanolic extracts (32.46%) were the most preferred extracts used in most studies followed by ethanolic (12.28%), ethyl acetate (10.53%), aqueous (7.89%), and chloroform (6.14%) ( Figure 6). The percentage was calculated as per report per species mentioned in Table 7. On the other hand, Figure 7 illustrates the types of plant parts most commonly used in the studies mentioned in Table 6. From the data shown, it can be suggested that the plant parts mostly studied are leaves (64%), roots (10%), stem bark (5%), and stem (5%). Only one work, published by Mondal et al. (2016), used latex and seed as plant samples to carry out anti-inflammatory, anticancer, analgesic, and anti-filarial activities and Wei et al. [93] conducted a test on the hypocotyl part to determine antioxidant property.  Figure 8 illustrates the types of assays usually conducted on mangroves. It is evident that antioxidant (28.8%) and antimicrobial (24.0%) assays were the two most common in vitro studies performed. Interestingly, most in vivo studies were done for antidiabetic assays compared to in vitro. It is found that antipyretic, antiviral, thrombolytic activity, anticoagulant, antiparasitic, antiulcer, and On the other hand, Figure 7 illustrates the types of plant parts most commonly used in the studies mentioned in Table 6. From the data shown, it can be suggested that the plant parts mostly studied are leaves (64%), roots (10%), stem bark (5%), and stem (5%). Only one work, published by Mondal et al. (2016), used latex and seed as plant samples to carry out anti-inflammatory, anticancer, analgesic, and anti-filarial activities and Wei et al. [93] conducted a test on the hypocotyl part to determine antioxidant property. On the other hand, Figure 7 illustrates the types of plant parts most commonly used in the studies mentioned in Table 6. From the data shown, it can be suggested that the plant parts mostly studied are leaves (64%), roots (10%), stem bark (5%), and stem (5%). Only one work, published by Mondal et al. (2016), used latex and seed as plant samples to carry out anti-inflammatory, anticancer, analgesic, and anti-filarial activities and Wei et al. [93] conducted a test on the hypocotyl part to determine antioxidant property.  Figure 8 illustrates the types of assays usually conducted on mangroves. It is evident that antioxidant (28.8%) and antimicrobial (24.0%) assays were the two most common in vitro studies performed. Interestingly, most in vivo studies were done for antidiabetic assays compared to in vitro. It is found that antipyretic, antiviral, thrombolytic activity, anticoagulant, antiparasitic, antiulcer, and anti-filarial tests were less seldom conducted. However, it is important to highlight that many      Gastric ulcers observed to decrease when glutathione is reduced in the gastric mucosa [115] Figure 8 illustrates the types of assays usually conducted on mangroves. It is evident that antioxidant (28.8%) and antimicrobial (24.0%) assays were the two most common in vitro studies performed. Interestingly, most in vivo studies were done for antidiabetic assays compared to in vitro. It is found that antipyretic, antiviral, thrombolytic activity, anticoagulant, antiparasitic, antiulcer, and anti-filarial tests were less seldom conducted. However, it is important to highlight that many mangrove species are used as a remedy for the ulcer in folklore medicine. For instance, the leaf of A. marina, the leaf of A. officinalis, the bark of B. cylindrica, bark, fruit, and leaf of C. decandra, whole plant of C. roxburghiana, and whole plant of R. mucronata (Table 5) are traditionally believed to cure ulcers. Nonetheless, the antiulcer potential of these named plants has not been extensively validated either in vivo or in vitro studies to confirm this belief in medical lore. A pie chart in Figure 9 represents mangroves that have been pharmacologically validated. The five most reportedly investigated species are R. mucronata (19%), A. officinalis (11%), A. marina (9%), B. gymnorhiza (8%), and R. apiculata (7%). It is important to highlight that B. gymnorhiza is the most traditionally used species (Figure 9), but it is found in the fourth place to be pharmacologically validated. This warrants an in-depth study on that particular species since its importance in folklore medicine.   A pie chart in Figure 9 represents mangroves that have been pharmacologically validated. The five most reportedly investigated species are R. mucronata (19%), A. officinalis (11%), A. marina (9%), B. gymnorhiza (8%), and R. apiculata (7%). It is important to highlight that B. gymnorhiza is the most traditionally used species (Figure 9), but it is found in the fourth place to be pharmacologically validated. This warrants an in-depth study on that particular species since its importance in folklore medicine.
A pie chart in Figure 9 represents mangroves that have been pharmacologically validated. The five most reportedly investigated species are R. mucronata (19%), A. officinalis (11%), A. marina (9%), B. gymnorhiza (8%), and R. apiculata (7%). It is important to highlight that B. gymnorhiza is the most traditionally used species (Figure 9), but it is found in the fourth place to be pharmacologically validated. This warrants an in-depth study on that particular species since its importance in folklore medicine.

Phytochemistry of Mangroves
Plants possess a plethora of novel and biologically active secondary metabolites and thus serves a reservoir for the production of novel drug compounds. In this era in which most researchers are

Phytochemistry of Mangroves
Plants possess a plethora of novel and biologically active secondary metabolites and thus serves a reservoir for the production of novel drug compounds. In this era in which most researchers are screening thousands of plants for the discovery of novel compounds, it is thus of high importance to scrutinize mangrove species with that very aim to isolate new phytochemicals which can be potential candidates for the development of pharmaceutical drugs. Saying so, about 200 bioactive metabolites have already been identified from mangroves [36,148]. Therefore, this prompts more studies for phytochemical screening of new metabolites. Phytochemical studies conducted on various mangrove species are summarized in Table 8. Histogram in Figure 10 illustrates the 16 most common types of phytochemicals isolated from mangrove species. Generally, the seven most common chemical constituents present are terpenoids (16.25%), tannins (12.5%), steroids (10.0%), alkaloids (9.38%), flavonoids (8.75%), saponins (8.75%), and glycosides (8.13%). Furthermore, mangroves also yielded other compounds namely fatty acid derivative, anthraquinone, amino acid, coumarin, quinine, ester, gum, phenol, terpene quercetin, and anthranoid. However, these compounds are found at low levels and are present in only certain mangrove plants. For example, the presence of fatty acids has been reported only in A. ilicifolius and A. marina but not in any other species (Table 8).
There is an undeviating link between phytochemicals and pharmacological activities. Kathiresan et al. [149] have shown that the bioactive compounds such as galactose, galactosamine, glucose, and arabinose possess significant anti-HIV activity. The different types of constituents present in medicinal plants are responsible for the wide range of pharmacological activities that the plants possess. It is reported that plants grown along the coastal regions are known to be potential resources of anticancer drugs [149]. For instance, the constituent tannin isolated from the species B. sexangula showed anticancer activity against Lewis lung carcinoma and Sarcoma 180 [149,150]. Additionally, the bark extracts of this mangrove species have shown antitumor activity which was due to the tannin-free aqueous residue containing the alkaloid, brugine, tropine, and its acetic ester acid [149]. Compounds produced by the species R. mangle also showed potent activity against carcinomas, melanomas, and lymphomas [149].
constituents present are terpenoids (16.25%), tannins (12.5%), steroids (10.0%), alkaloids (9.38%), flavonoids (8.75%), saponins (8.75%), and glycosides (8.13%). Furthermore, mangroves also yielded other compounds namely fatty acid derivative, anthraquinone, amino acid, coumarin, quinine, ester, gum, phenol, terpene quercetin, and anthranoid. However, these compounds are found at low levels and are present in only certain mangrove plants. For example, the presence of fatty acids has been reported only in A. ilicifolius and A. marina but not in any other species (Table 8). There is an undeviating link between phytochemicals and pharmacological activities. Kathiresan et al. [149] have shown that the bioactive compounds such as galactose, galactosamine, glucose, and arabinose possess significant anti-HIV activity. The different types of constituents present in medicinal plants are responsible for the wide range of pharmacological activities that the plants possess. It is reported that plants grown along the coastal regions are known to be potential resources of anticancer drugs [149]. For instance, the constituent tannin isolated from the species B. sexangula showed anticancer activity against Lewis lung carcinoma and Sarcoma 180 [149,150]. Additionally, the bark extracts of this mangrove species have shown antitumor activity which was due to the tannin-free aqueous residue containing the alkaloid, brugine, tropine, and its acetic ester acid [149]. Compounds produced by the species R. mangle also showed potent activity against carcinomas, melanomas, and lymphomas [149].
Barik et al. [121] were the first to isolate a flavone known as 5,7-dihydroxy-2-(3-hydroxy-4, 5dimethoxy-phenyl)-chromen-4-one-a, from the leaves of B. gymnorhiza. It has been reported that the compound was responsible for anti-inflammatory activity with a percentage inhibition of 80% against COX-2 mediated prostaglandin E2 production. Phenol group is a bioactive chemical compound that shows good antioxidant activity. High antioxidant activity was exhibited by the methanolic fruit extract of B. gymnorhiza with an IC50 value of 13.47 ppm. The fruit is rich in carbohydrate (29.28%) and thus can become a potential food source [64,151]. Sur et al. [64] reported that polyphenols such as gallic acid, quercetin and coumarin isolated from the methanolic leaf extract showed significant antioxidant activities. These constituents help in nursing the injury of hepatic tissue through its Barik et al. [121] were the first to isolate a flavone known as 5,7-dihydroxy-2-(3-hydroxy-4, 5-dimethoxy-phenyl)-chromen-4-one-a, from the leaves of B. gymnorhiza. It has been reported that the compound was responsible for anti-inflammatory activity with a percentage inhibition of 80% against COX-2 mediated prostaglandin E2 production. Phenol group is a bioactive chemical compound that shows good antioxidant activity. High antioxidant activity was exhibited by the methanolic fruit extract of B. gymnorhiza with an IC 50 value of 13.47 ppm. The fruit is rich in carbohydrate (29.28%) and thus can become a potential food source [64,151]. Sur et al. [64] reported that polyphenols such as gallic acid, quercetin and coumarin isolated from the methanolic leaf extract showed significant antioxidant activities. These constituents help in nursing the injury of hepatic tissue through its antioxidant effects. Moreover, constituents mainly flavonoids, reducing sugars, gums, saponins, and tannins isolated from the roots of B. gymnorhiza are responsible for antinociceptive and antidiarrhea properties [152].

Acanthus ilicifolius
A. ilicifolius is a small tree of height up to 2 m with stilt roots, sharp edges leaves, kidney-shaped fruits, and large light-violet petals [42]. A. ilicifolius is found in Bangladesh, India, and South Thailand [33,65,68]. It is widely used as a traditional medicine by the local people in these countries. In Bangladesh and India, the whole plant parts are used for treating rheumatism, hepatitis, leprosy, skin allergies, snake bites, diabetes, asthma, kidney stones, smallpox, and ulcer (Table 5). In South Thailand, this species is used to treat psoriasis [70].
A. ilicifolius is found to have many pharmacological activities; namely, the methanolic leaf extracts have good antioxidant, anti-inflammatory activities [66,105]. Acetone leaf extracts showed good antimicrobial activities. A wide array of phytochemical constituents is found to be present in different parts of the plants namely the leaves, barks, roots, and fruits. Results from GC/MS confirmed the presence of alkaloids (acanthicifoline (3), benzoxazin-3-one (6)), flavonoids, steroids (cholesterol (51), β-sitosterol (54)), glycosides, saponins, tannins, and terpenoids [42,155,156] (Table 8). Ribose derivative isolated from this mangrove species known as 2-benzoxazoline exhibited antiviral and antitumor activities [150]. Recently, a new sugar ester was derived from the roots of A. ilicifolius known as 1,2-di-(syringoyl)-β-d-glucopyranose [157]. The structure of the new compound was clarified by extensive spectroscopic methods such as NMR and HRESI-MS.

Aegialitis rotundifolia
A. rotundifolia is a small tree originating from the Plumbaginaceae family with a height of 2-3 m. It has broad and ovate leaves, 5-8.8 cm long and 4.5-8.5 cm wide [44,45]. The species is mainly grown in Bangladesh and is used to cure inflammatory and painful arthritis [72,73]. The leaf infusion is used as an anti-ache agent. A. rotundifolia showed moderate inflammatory and anti-pyretic activities with aqueous leaf extracts [73]. Moreover, with recent literature, methanolic leaf extracts showed thrombolytic and membrane stabilizing activities. Additionally, the extracts did not show any antibacterial activity as the test sample was resistant against both gram-positive and gram-negative bacteria [45]. Ghosh et al. [160] identified compounds comprising of alkaloids, carbohydrates, tannins, phenolic compounds, sterols, triterpenoids, saponins, and flavonoids from the ethanolic leaf extracts.

Aegiceras corniculatum
A. corniculatum originates from the Primulaceae family with a height of up to 7 m. It has alternate and obovate leaves, 3-10 cm long and 1.5-5 cm wide. Its fruit is green to pink in color and has a curved-cylindrical shape [43]. Folk medicinal practitioners from the Sindh region in Pakistan use the stem to treat rheumatism, painful arthritis, and inflammatory diseases [74,75]. A. corniculatum showed many potential pharmacological activities (Table 6). For instance, the in vivo antinociceptive activity was investigated by Roome et al. [74,75] using acetic-acid induced writhing in mice. The ethyl acetate stem extracts at 50 mg/kg showed an inhibition of 53 ± 3.0% while the hexane stem extract at the same concentration has an inhibition of 28 ± 2.5%. Janmanchi et al. (2017) conducted an antibacterial study using REMA assay. It was found that the crude leaf extract was active against Bacillus subtilis and Escherichia coli. With the same extract, the antioxidant study was conducted using DPPH assay, and the IC 50 value was 1.79 ± 0.0002 mg/mL. However, Roome et al. [74] mentioned that A. corniculatum lacked pharmacological evaluation concerning its analgesic effects. Using standard phytochemical tests, analysis of the bark, stem, and leaf extracts showed the presence of alkaloids, amino acids, benzoquinones, tannins, coumarins, flavonoids, saponins, and glycosides, among others (Table 8).

Acrostichum aureum
This species is found in Kerala, India. The local people used the whole plant as a worm remedy and as an astringent for hemorrhage [76]. Thomas [76] investigated the antibacterial activity of methanol, acetone, petroleum ether, and water leaf extracts against Escherichia coli, Serratia marcesens, Pseudomonas aeruginosa, and Staphylococcus aureus. The petroleum ether and water leaf extracts were inactive against Escherichia coli and Serratia marcesens while acetone leaf extract was active against all the tested microorganisms. In the methanol, acetone, petroleum ether, and water leaf extracts, alkaloids were reported absent whereas flavonoids and phenols were found present [76].

Avicennia
A. marina is a medium length mangrove tree from the Acanthaceae family with a height of 14 m with a specialized root structure known as pneumatophores. Its bark is smooth with thin, stiff, and brittle flakes in the surface and is generally light grey. The leaves are thick and glossy and 5-8 cm long. The species produces green and oval-shaped fruits [7,46]. A. marina is widely distributed in Australia, South-East Asia, Madagascar, Mozambique, and along the coastline of Africa [7]. This species traditionally used to manage smallpox, skin diseases, ulcers, and throat pains [65] and it has many pharmacological properties such as antimicrobial, anti-inflammatory, antiviral, antimutagenic, anticancer, and antioxidant (Table 6). Ramanathan [114] investigated the antimicrobial activity of the crude leaf extract using disc diffusion assay against S. aureus, Klebsiella aerogenes, P.s aeruginosa, Bacillus subtilis, E.a coli, Enterobacter aerogenes, Proteus sp, Salmonella parathyphi, and Citrobacter sp. The extracts showed activity against all the tested microorganisms. Shafie et al. (2013) conducted the anti-inflammatory activity on the rat model, and it was observed that the inflammatory markers were reduced, and the joint lesions were also improved. The ethanolic leaf extracts were active against HIV (Human immunodeficiency virus), SFV (Semliki forest virus), EMVC (Encephalmyocarditis virus), and HBV (Hepatitis B virus) [98]. The phytochemical screening of the methanolic, ethanolic, ethyl acetate, ethyl ether, and water extracts indicated the presence of a wide array of constituents viz; alkaloids, 31 glycosides, phenols, 5 terpenoids, saponins, 14 flavonoids, 23 tannins, 19 naphthalene derivatives, 6 fatty acids, and 7 steroids and amino acids [7] (Table 8).
A. germinans is the tallest mangrove tree compared to the other Avicennia species such as A. integra, A. bicolor, A. marina, A. officinalis, and A. schaeurina. This species comes from the Acanthaceae family. It is 30 to 50 m tall with rough and irregular scales on the bark. These plants have opposite and elliptical leaves which are 3-15 cm long. It produces dark-green, flat propagules with velvety pericarp which are 2-3 cm in diameter [7]. The bark, leaf, and flower of A. germinans are used traditionally to treat malaria, haemorrhoids, rheumatism, swellings, throat pains, and hemorrhage [7,77]. In the Bahamas, A. germinans is traditionally used to restore vitality and to manage rheumatism while in Colombia, gargling the bark decoction helps to cure cancer of larynx and ulcers of the throat [77]. The methanol extract of A. germinans exhibited significant antibacterial activity against Escherichia coli, Klebsiella sp, Proteus sp, Staphylococcus aureus, Pseudomonas sp., and Salmonella sp. Fennell et al., (2004) reported that the antibacterial properties are due to the presence of tannins, alkaloids, flavonoids, terpenoids, or essential oils. The compounds identified from A. germinans originate from the phytochemical class of glycosides namely 2 -cinnamoyl-mussaenosidic acid (108), 2 -caffeoyl-mussaenosidic acid, and 2 -CoU mamaheswarraoroyl-mussaenosidic acid [7,161,162].
A. integra is the smallest mangrove tree with a height of 2-7 m in the Avicennia genus. It has pneumatophore roots system with smooth bark, brown to reddish. The leaves are opposite, simple, and elliptical with shiny surfaces of length 5-14 cm. The plant produces pale green fruits, 21-23 mm long and 12-15 mm wide. This species also blooms to produce golden yellow or orange zygomorphic flowers. The plant can be found along the coastline of Australia [7].
A. bicolour originates from the Acanthaceae family and is 8-20 m tall. It is widely distributed in Colombia, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Panama, and Nicaragua [7].
A. schauerina species comes from the same family of Acanthaceae as the other Avicennia mangrove trees. The produced fruits are pale sap green with a purple tinge and are flatter compared to A. germinans. A. schauerina produced flowers which are larger than the flowers produced by A. bicolor [7].
A. officinalis is 30 m tall with pneumatophore roots system, smooth bark which is dirty green to dark grey, and is slightly fissured but does not flake compared to A. germinans [47]. The leaves are shiny, green in color with round apex, 10 cm long, and 5 cm wide. The tree has pneumatophores similar to the other Avicennia species. The flower of A. officinalis is the largest of all the species in its genus and is orange-yellow to lemon-yellow. This species produced a heart-shaped propagule, green or brown [7,47]. A. officinalis is an evergreen mangrove tree distributed throughout India, Bangladesh, Indonesia, Brunei, Myanmar, Vietnam, and Southern Papua New Guinea (Hossain et al., 2016). In Bangladesh, the species is known as 'DholaBaen'. Locally, it is used as a treatment for boils and tumors (Hossain et al., 2016) and the unripe seeds are poulticed onto the sores of smallpox, boils, and abscesses [156]. Additionally, the bark can be used to heal scabies (Hossain et al., 2016). A decoction of the plant mixed with sugar candy and cumin is used against dyspepsia. The local people traditionally use the resin produced by the plant as a contraceptive without side effects [80]. A. officinalis is largely studied for its pharmacological activities. For instance, the ethyl acetate leaf extract is analyzed for its antimicrobial activity against E. coli, Streptococcus mutans, S. aureus, Aspergillus flavus, and Trichophyton rubrum. The extract showed activity against E. coli, S. mutans, and S. aureus but found inactive for A. flavus and T. rubrum. Anti-ulcer activity was investigated on the ethanolic extract using indomethacin-induced gastric ulcer assay and it was observed that the gastric ulcers decreased when the amount of glutathione is reduced in the gastric mucosa [115]. Hossain et al. (2012) investigated the diuretic and neuropharmacological properties of the methanolic leaf extracts. The Lipschitz diuretic model was used to test the diuretic activity of the sample. For the dosage of 200 and 400 mg/kg, the volume of urine excreted was 3.06 ± 0.18 mL and 3.89 ± 0.13 mL, respectively. It is reported that the amount of Na + ion excreted by the methanolic extract is higher compared to the excretion of K + ion and as a result the plant is classified as a good diuretic which causes less hyperkalaemic side effects. In GC/MS analysis, the methanolic, ethanolic crude leaf extract showed the presence of alkaloids, terpenoids, glycosides, tannins, steroids, flavonoids, naphthalene derivatives, reducing sugar, sterols, fatty acids, gums, wax esters, and amino acids, among others. Thatoi et al. [7] identified 17 compounds from the terpenoid class of constituents as taraxerol (96) Table 8).

Bruguiera
This species has not received enough scientific attention concerning its morphological characteristics, traditional uses, and pharmacological properties. However, Revathi et al. [88] and Bandaranayake [65] reported that the stem and bark of the plant consist of sulfur-containing alkaloids.
B. cylindrica coming from the Rhizophoraceae family, is 20 cm tall with pneumatophore roots and has smooth bark, grey with corky raised patches containing lenticels. The leaves are glossy in appearance and elliptical in shape with pointed apex. The plant produces fruits of 15 cm long and has a curved-cylinder shape. This species blooms greenish-white flowers in clusters of two to five [48]. The bark of B. cylindrica is traditionally used to treat hemorrhage and ulcers by the local people of India [63]. The IC 50 values for the methanolic leaf and stem extracts are 175 and 162.5 µg/mL, respectively [120]. Laphookhieo et al. [163] conducted phytochemical screening on the fruit of B. cylindrica and the pentacyclic triterpenoids esters identified are E-feruloyltaraxerol (147), 3α-Z-feruloyltaraxerol (148), 3β-E-feruloyltaraxerol (149), 3β-Z-feruloyltaraxerol (150), 3α-E-coumaroyltaraxerol (151), and 3α-Z-coumaroyltaraxenol (152). Gawali and Jadhav [120] reported the presence of tannins, saponins, alkaloids, triterpenoids, anthraquinone, and flavonoids in the leaves of the plant.
The bark of this mangrove tree is used to manage diabetes [61]. Bunyapraphatsara et al. [123] performed antioxidant tests on the ethyl acetate leaf extract using three different methods namely DPPH, lipid peroxidation inhibition, and quinone reductase induction activity. Using the DPPH assay, the resulting EC 50 values of the young pods and the leaves are 5 and 105 µg/mL, respectively. With lipid peroxidation inhibition assay, the IC 50 values of the young pods and leaves are 0.375 and 42.6 µg/mL, respectively. Also, while using the third method, which is quinone reductase induction assay, the IC 50 values recorded were >20 µg/mL for both young pods and leaves samples. Comparing the IC 50 values from the two methods (lipid peroxidation inhibition and quinone reductase induction), it can be said that the samples showed better inhibition with the quinine reductase induction assay. Arora et al. [101] reported the presence of phenolic compounds in the bark of B. parviflora. Revathi et al. [88] reported the presence of tannins and triterpenes in the bark and leaves of the plant.
B. sexangula is scarcely distributed on the north shore and sides of Oahu, Hawaii [186]. Revathi et al. [88] reported the presence of phenolics, steroids, alkaloids, and tannins in the bark of this species. Alkaloid (1,2-dithiolane) of this plant exhibited antitumor activity against Sarcoma 180 and Lewis [150].
B. gymnorhiza is a common mangrove tree reaching a height of up to 15 m and originates from the Rhizophoraceae family. Its bark is smooth and grey-brown in color. It has smooth and glossy leaves with pointed apex, 9.5-20 cm long and 3-7 cm wide. The propagules are green in color and have a cigar-shape which is 5-12 cm long and 1-2 cm wide. The flowers of the plant have pale yellow-green to pinkish orange sepals [187]. B. gymnorhiza is a well-known mangrove tree. This species is distributed in the wild forest of India (Sunderbans), throughout Malaysia, China, Indonesia, Comoros, and Mauritius. In India, the bark and root decoction is used to treat diabetes, fever, and diarrhea [81,82]. In Malaysia, the local people used its stem as a remedy for viral fever [83]. In the Guangxi Province of China, the leaves and fruits are traditionally used to cure burns, intestinal worms, liver disorders, and diarrhea [33,54]. The folk medicine practitioners in Indonesia uses the fruits to treat eye disease, malaria, and shingles, which is a viral infection that can occur anywhere on the body [85]. In Comoros and Mauritius Islands, a decoction is prepared by boiling root (15 cm length) of B.gymnorhiza and five to seven leaves of P. borbonense in two cups of water. The decoction is taken to manage diabetes, hypertension, and hemorrhage [13]. The leaves, roots, and barks of this species have been reported to possess many medicinal properties ( Table 5). The methanolic leaf extract has been studied for its antinociceptive activity using acetic acid-induced writhing in mice. At dosage 250 and 500 mg/kg, the % writhing inhibitions were 46% and 59%, respectively. The extract showed significant inhibition compared to the standard drug diclofenac sodium and confirmed the antinociceptive activity [81]. Barik et al. [121] investigated the anti-inflammatory activity on the crude leaf extract using COX (cyclooxygenase) inhibition assay. The %inhibitions at dosage 10 and 10 µg/mL were 9.7 ± 7.2% and 65.1 ± 5.8%, respectively. The ethanolic root extract was reported non-toxic with no significant change in behavior or neurological response up to 400 mg/kg body weight [82]. Methanolic leaf extract was found active against Escherichia coli (22 mm), while the hexane bark extract showed a broader spectrum of antimicrobial activity against K. pneumonia (23 mm), S. typhi (22mm), Staphylococcus aureus (19 mm), and Shigella flexneri (22 mm), respectively [62]. The plant was also reported to exhibit antioxidant, antihyperglycemic, anti-diarrheal, and hepatoprotective activities [64,[81][82][83]105] (Table 7). Phytochemicals present in the leaves, stems, flowers, roots, and fruits include flavonoids, saponins, reducing sugars, tannins, gums, dammarane triterpenes, aromatic compounds, sterols, diterpenoids, anthocyanins, and catechins, among others (Table 8). Rahman et al. [164] identified the compounds from the dammarane triterpenes class as Bruguierol A-C (153-155), 4-hydroxy-dithiosulfonate, bruguiesulfurol (156), 4-hydroxydithiolane 1-oxides, brugierol (157), and isobrugierol (158).

Ceriops
The whole plant of C. roxburghiana species is traditionally used to treat diabetes and ulcers. The tree originates from the Rhizophoraceae family. Phytochemical screening of the whole plant revealed the presence of gibberellins and procyanidins [88].
C. tagal comes from the Rhizophoraceae family and grows to a height of 25 m. It has a buttress root system, smooth barks, and is silvery-grey to orangish-brown with lenticels on its surface. The leaves are obovate and yellowish-green on the bottom surface, and they are 6 cm long and 3 cm wide. The propagule is ovoid in shape, brown in color, and is generally 3 cm long [57]. The bark of this plant is traditionally used to treat hemorrhage [61]. Chen et al. [170] identified six compounds from the root extract as 8 (14) (Table 8).

Excoecaria agallocha
This species is also known as the blind-your-eye mangrove plant. This is because the latex produced by the bark is poisonous and can cause temporary blindness. E. agallocha comes from the Euphorbiaceae family and is 15 m tall. Its root system is described as elbow shaped pegs. The leaves are alternate and elliptical, with an acuminate apex and narrow base. They are 3-8 cm long and 1.5-3 cm wide [50]. This tree is known to produce latex which has therapeutic effects. The plant is traditionally used to treat rheumatism, epilepsy, leprosy, ulcers, and paralysis. This species is widely distributed from India, Africa, to northwest Australia. The local people of India, New Caledonia, and Malaysia traditionally used the latex and leaves to cure dart and fish poisoning. In Pakistan, besides using it for ulcers, paralysis, rheumatism, and leprosy, the latex is used as an abortifacient [174]. In Tamil Nadu, the latex is also used to alleviate a painful toothache [58]. This mangrove species possesses many pharmacological activities namely antioxidant, anti-inflammatory, analgesic, anticancer, anti-filarial, and antimicrobial activities (Table 7). Mondal et al. [50] investigated the anti-inflammatory activity on the stem extract using two different methods namely carrageenan-induced paw edema test and pellet-induced granuloma test. The ethanol and water (3:1) extract of the plant showed a significant inhibition of 62.29% in carrageenan-induced paw edema model while the pellet-induced granuloma test showed an inhibition of 57.03% with the stem extract. Analgesic activity was tested using acetic acid-induced writhing test in mice. At dosage 500 mg/kg, the ethanol and water (3:1) bark extract showed the highest activity with a reduction of 53.87%. The antimicrobial properties of E. agallocha were tested by Bakshi and Chaudhuri [106] using disc-diffusion assay and the results showed the extract was active against E. coli, A. tumefaciens, S. mutans, and S. aureus but inactive against A. flavus and T. rubrum. A study by Mondal et al. [50] revealed a wide array of phytoconstituents isolated from E. agallocha (Table 8). The main constituents identified were flavonoids, terpenoids, diterpenes, alkaloids, and tannins [50,88,[174][175][176].

Heritiera
H. fomes is a tall mangrove tree which can attain a height of 15-25 m. It comes from the Sterculiaceae family and has pneumatophore roots, elliptical leaves, and blooms bell-shaped flowers pink to orange in color [51]. In Bhitarkanika and Sunderbans, India, the leaves, roots, and stems are traditionally used to treat cardiovascular diseases, gastrointestinal disorders (diarrhea, dyspepsia, stomach ache, dysentery, constipation), and skin diseases (rash, eczema, boils, itch, sores) [7,51,89,90]. Ali et al. [91] and Rahmatullah et al. [69] also reported that the whole plant or twig could be used against bloating, diabetes, heart disease, hepatic disorders, goiter, toothache, and oral infection. H. fomes showed antihyperglycemic, antidiabetic, and antinociceptive activities in the methanolic bark extract ( Table 7). The ethanolic leaf extract showed excellent antimicrobial activity against E. coli, S. typhi, S. paratyphi, and S. aureus [51]. Rahmatulla et al. [69] conducted the toxicity test on the leaf extract and the % writhing inhibitions at dosage 250 and 500 mg/kg was 34.83% and 59.20%, respectively. The ethanolic leaf extract, bark extract, and the acetone and aqueous stem extracts were screened for the phytochemical compositions, and the constituents mainly include alkaloids, cardiac glycosides, tannins, steroids, saponins, gums, carbohydrates, proteins, and amino acids, among others (Table 8).

Lumnitzera racemosa
This mangrove tree is used traditionally by the local people of Orissa, India, to treat rheumatism, skin allergies, asthma, diabetes, snake bites, and as a blood purifier [95]. L. racemosa showed antioxidant, cytotoxicity, and anticoagulant properties (Table 7). Cytotoxicity test was conducted on the aqueous leaf extract against Hep G2 cancer cell line using MTT assay. The resulting IC 50 value was 26.05 µg/mL, and the extract was reported to exhibit potent cytotoxicity activity on the Hep G2 cell lines [127]. The aqueous leaf, methanolic twig, and dichloromethane: methanol stem extracts were screened for phytochemicals and most constituents present were alkaloids, phenols, flavonoids, terpenoids, tannins, sterols, carbohydrates, quinines, saponins, quercetin, and aromatic ester [127,167,177].

Kandelia
K. candel originates from the Rhizophoraceae family and grows to a height of up to 10 m. It has flaky barks with lenticels on its surface and is reddish-brown. The plant produces oval-shaped fruits, 25 cm long and blooms white flowers [57]. K candel is distributed along the tropical and subtropical coastline of China and from western India to Borneo [93]. The plant is traditionally used to treat cardiovascular diseases, cancer, and neurodegenerative disorders. The leaf extract of this mangrove species is reported to possess excellent antioxidant activities. The ethyl acetate hypocotyl extract has an IC 50 value of 124.19 ± 3.02 µg/mL with DPPH assay and an AAE value of 4.39 ± 3.17 mmol/g with FRAP (Ferric reducing antioxidant power) assay [93].
K. rheedii has been used for tuberculosis treatment in India [94]. Revathi et al. [88] reported the presence of steroids and triterpenoids in the bark, leaf, and fruit extracts.
10.12. Nypa fruticans N. fructicans, also known as Nypa palm, is a 9-m tall prostate-stemmed gregarious palm originating from the Arecaceae family. The leaves have a palm-like structure. It is distributed in Queensland (Australia), India [180], and Malaysia [179]. This mangrove palm is reported to have received little scientific attention. In Malaysia, the local inhabitants used the plant to manage diabetes [96] and in Philippines, the flowers and leaves are traditionally used to treat diabetes and snake bites [61]. The methanolic leaf extract showed antimicrobial activity against E. coli, A. tumefaciens, S. mutans, and S. aureus while the extract was inactive against A. flavus and T. rubrum [106]. The antioxidant activity of ethyl acetate extract was investigated for its antioxidant activity using DPPH assay, and the result showed an IC 50 value of 2.770 ± 0.012 mg/mL [96].
R. mucronata, also known as red mangrove, loop-root mangrove, or Asian mangrove, is a 20-25 m tall mangrove tree and form part of the Rhizoporaceae family. The species has stilt roots buttressing the trunk. It has dark green thick leaves with a distinct mucronate tip and covered with minute black spots on the inferior surface. The mangrove tree produces green fruits with a cigar shape. The flowers are creamy white in color [13]. The plant is found to be present in many countries across the globe. R. mucronata is native to Africa (Egypt, Ethiopia, Kenya, Madagascar, Mauritius, Mozambique, Tanzania, Somalia, South Africa, Sudan), Seychelles island, Asia (India, Papua New Guinea, Sri Lanka, Philippines, Thailand, Taiwan, Vietnam), South Pacific (Solomon Islands, Vanuatu), and Australia (Queensland, Northern Territory). This mangrove species has many beneficial medicinal properties. For instance, in Tamil Nadu, India, the bark or the whole plant is traditionally used to cure angina, dysentery, hematuria, hepatitis, ulcers, diabetes, hemorrhage, vomiting, and nausea. In Mauritius, the local inhabitants use the R. mucronata plant as a traditional medicine against diabetes, hypertension, and also as a natural remedy to reduce the level of urea in the blood. A tea is prepared using root (5 cm length) of R. mucronata, 3 whole plants of Bidenspilosa, 10 leaves of P. borbonense, bark (15 cm length) of Erythroxylum laurifolium, 15 leaves of Aphloia jobi, and 10 leaves of Antidesma madagascariense. The tea is taken to balance the level of urea in the blood [13]. The root decoction is used to manage diabetes and hypertension while the leaf infusion can be used for fever. The Indonesians traditionally sued the whole plant as a treatment for elephantiasis, haematoma, hepatitis, ulcer, and febrifuge [60,61]. In China and Japan, the bark is used against diarrhea [99]. In Papua New Guinea, the local people used the stem to stop constipation, cure fertility and menstruation disorders [59]. R. mucronata possesses many pharmacological properties namely antioxidant, anti-inflammatory, anti-bacterial, antimicrobial, antidiabetic, analgesic, anti-HIV, and anti-cholinesterase properties (Table 7). Chakrarborty and Raola [137] conducted the antioxidant study on the crude chloroform leaf extract using DPPH assay and the resulting IC 50 value was 1.38 ± 0.03 mg/mL, while Suganthy and Devi [100] conducted the same assay to obtain an IC 50 value of 47.39 ± 0.43 µg/mL. Interestingly, a study conducted by Hardoko [144] reported that the ripe flour of the fruit contains 7.50% soluble dietary fiber and 38.60% insoluble dietary flour. Additionally, the antidiabetic in vivo study conducted showed a decline in the blood glucose level, which, as a result, makes the ripe flour of R. mucronata a good functional food for diabetic patients. Recently, Aljaghthmi et al. (2018) showed that the bioactive compounds present in this mangrove species contribute in lowering blood sugar level and boosting insulin production. Pimpliskar et al. (2012) investigated the antimicrobial activity on the ethanolic stem extract. However, to the best of the knowledge of the authors, no other studies were conducted on ripe flour to support or confirm these results obtained by Hardoko [144]. Alikunhi et al. [145] added that the antidiabetic properties of R.mucronata, R.apiculata, and R. annamalayana were due to the presence of the insulin-like protein present in the leaves. R. apiculata was more potent compared to the other two Rhizophora species since the results were in equivalence with the control drug, glibenclamide. The extract inhibited activity against E. coli (16 mm), S.s aureus (15 mm), S. typhi (20 mm), S. pyogenes (12 mm), and P.s aeruginosa (15 mm), respectively. However, no inhibition was noted against K. pneumonia, P.s vulgaris, and C. albicans. The different plant parts of R. mucronata contain a wide variety of phytochemicals namely condensed tannins, polyphenols, lipids, inositol, gibberellins, alkaloids, tannins, and proteins, among others [58,60,88,137,167] (Table 8).
R. mangle comes from the Rhizophoraceae family and attains a height of 24 m. It has stilt roots, thin and smooth bark grey or grey-brown in color. The leaves are elliptical in shape, thick, shiny green on the upper surface, and yellow-green with black spots on the bottom surface [56]. In India, the leaf and bark are used traditionally to manage diabetes [88,101]. R. mangle possessed antioxidant and anti-ulcer activities (Table 6). Andrade-Cetto et al. (2017) isolated six compounds from the ethanolic cortex extract, namely Cinchonains Ia and Ib, catechin-3-O-rhamnopyranoside, lyoniside, and nudiposide using NMR, UPLC-DAD-MS, HPLC, and the standard TLC techniques. Revathi et al. [88] and Kandil et al., (2004) reported the presence of tannins, triterpenes, flavonoids, glycosides, quercetin, myricetin, and kaempferol diglycosides in the bark and leaf extract.
R. racemosa originates from the Rhizophoraceae family. It has a height of up to 30 m, stilt roots, and elliptical leaves [26]. Revathi et al. [88] reported the presence of tannins and steroids in the flower and leaf extract of that plant. This mangrove species has been evaluated for its lethal dose (LD 50 ) which is commonly used as a toothache remedy by the Nigerian people [102].
R. stylosa is a mangrove tree from the Rhizophoraceae family with a height of up to 15 m. Its bark is dark brown to black. It produces ovoid to pear-shaped propagules and is generally 4 cm long [57].  (128), cinchonain Ib (268), and proanthocyanidin B2. Revathi et al. [88] reported the presence of inositols and steroids in the leaves, roots, and seeds extract.

Xylocarpus granatum
This species is a small mangrove plant of height 3-8 m with a buttress root system. It has a light brown, yellowish, or greenish bark, and is smooth and flaky. The leaves are bright light green to dark green with a round apex [24]. The mangrove species occurs mainly in the Indian Ocean and Southeast Asia [185]. In East Africa and South Asia, the local people use the bark and leaf as a natural remedy for cholera, diarrhea, fever, and malaria [58,104]. X. granatum has many pharmacological activities namely antioxidant, anticancer, antidiarrheal, and antimicrobial (Table 7). Das et al. [104] investigated the antimicrobial activity on the ethanolic stem extract against seven bacterial pathogens, namely E. coli, E. aerogenes, P. aeruginosa, S. typhi, S. aureus, K. pneumonia, and V. cholera. The extract was active against all tested microorganisms. Wu et al. [185] isolated three new limonoids, namely 2,3-dideacetylxyloccensin S (281), 30-deacetylxyloccensin W (282), and 7-hydroxy-21b-methoxy-3-oxo-24,25,26,27-tetranortirucalla-1,14-diene-23(21)-lactone (283) from the seed of the Chinese mangrove, X. granatum (Table 8).

Conclusions and Future Perspectives
This review attempts to project the importance of various mangrove species used traditionally. An overview of their ecological aspects is also given since these plants represent a symbolic plant for the marine ecosystem. The fundamental ecological roles mangroves species play need to be understood to safeguard our environment as these species and their habitats are threatened due to rapid coastal development, extensive aquaculture, climate change scenarios, and overharvesting [9]. So far, there have been piecemeal reviews on mangroves dealing with one aspect or one species at a time but none of them have systematized all the traditionally known mangroves under one review. For instance, Rahmatullah et al. [69] evaluated botanical features and phytochemical profiling of only one mangrove species, B. gymnorhiza. Bandaranayake [33,65] [189] focused on mangroves from Pichavaram (India) only, while Mondal et al. [50] documented only one species, E. agallocha. Patra and Mohanta [190] have reported only the antimicrobial aspects of a few mangroves, and Simlai and Roy [147] elaborated on biological activities and chemical constituents from mangroves in only a specific region of the Sundarban estuary. This review article provides a more extensive coverage on all mangroves by compiling updated information and data on their discovery, ecology and physiological aspects, types, geographical distribution, taxonomy, morphological characteristics, ethnopharmacology, pharmacological activities, and phytochemical evaluation.
Morphologically, mangroves are defined as small trees or shrubs growing along the coastlines in muddy or rocky soils. For instance, Kathiresan and Bingham [6] classified mangroves as halophytes, however Collins, Merriam-Webster, and the Oxford English dictionaries defined mangroves simply as trees or shrubs with tangled roots growing along the coastlines of tropical countries while Spalding [14] generalized mangroves as trees or large shrubs growing in or adjacent to intertidal regions which can easily adapt themselves in their environment. Having said that, it can be concluded that there are still ambiguities in the definition of mangroves and thus require the attention of botanists to properly define the plant. In many countries, particularly in India, people believed that mangroves can cure a wide spectrum of diseases such as rheumatism, diabetes, fever, and gastrointestinal disorders (diarrhea, dysentery, dyspepsia, constipation). Locally, the Mauritian people have used the plant as a traditional medicine for diabetes and hypertension for many years. Interestingly, mangroves are not only important for people but equally significant for animals. For instance, a study conducted by Gardner [16] in Madagascar showed that lemurs use mangroves as their prime natural habitat for sleeping and foraging [16].
From the literature, it is acknowledged that there are 84 mangrove species. However, only 27 species are known to the folklore medicine and not all species have been tested for their pharmacological activities both in vivo and in vitro, which accounts for only about 31% of mangrove species that have been investigated till date. This rather low percentage can be linked to either a poor interest from the researchers' side on these particular plants or because these plants are considered as endangered species in some countries. Therefore, this might have created a gap between traditional medicines and the interest in developing drugs derived from mangroves. Consequently, to fill the gap between traditional medicines and pharmaceutics, more research is needed to provide a greater range of potential cures against a panel of diseases.
So far, we have seen that mangrove species has a long history in traditional medicine/ ethnopharmalogy and is still widely used because of a wide array of potential sources of natural compounds. Several classes of bioactive substances have been isolated and identified and investigations on different metabolic activities have been performed both in vitro and in vivo. While we present and discussed herein evidence in connection with mangrove species and their beneficial medicinal properties, there are still doubts as to how far these bioactive compounds can be used as direct disease management agents. There is no conclusive report of human trials and up to what extent these beneficial medicinal properties are substantiated warrant further investigation. For proper ethnopharmacological use of mangroves, we believe there should be more direct scientific evidence substantiated with more clinical-based research with rationale impact assessed on human health.
A deeper scientific understanding of the mechanisms of those compounds, their molecular targets, and any drug interaction should be further investigated. Well-designed in vivo tests and randomized controlled clinical studies should be carried out to obtain statistically significant outcomes. There is also a dire need to ensure the efficacy and safety of mangrove preparations and not direct their use solely based on people's perceptions. Other pertinent questions that must be delved in are: How far can these mangroves be further exploited on a commercial scale by pharmaceutical companies? What are the optimized methods of extraction and characterization? What are the risk levels or adverse human effects? What types of pharmacological evaluations must be carried out to confirm activity of mangrove ingredients?