AN ANNOTATED CHECKLIST OF THE VASCULAR FLORA OF COASTAL MANGROVE ECOSYSTEMS OF BARGUNA DISTRICT, BANGLADESH

This study provides the basic taxonomic data on the vascular flora of the coastal mangrove ecosystems in Barguna district of Bangladesh. Plant samples and field data have been collected following walk through method. The present study reveals the occurrence of 532 species under 378 genera and 112 families in the study area, of which 24 are true mangroves, 46 mangrove associates and 461 non-mangroves. The pteridophytes are composed of 22 species under 20 genera of 12 families and gymnosperms of two species under two genera and two families. Magnoliopsida are composed of 375 species under 279 genera and 77 families, and Liliopsida of 133 species belonging to 77 genera under 21 families. Fabaceae with 28 species is recorded as the largest dicot family, followed by Asteraceae, Apocynaceae, Euphorbiaceae and Malvaceae. Poaceae with 45 species is the largest monocot family, followed by Cyperaceae, Araceae and Arecaceae. About 60.15% of these species are herbs, 21.80% trees, 15.79% shrubs, 1.88% palms and 0.38% bamboos. The study area composed with 74.06% native and 25.94% exotic species, 79.70% species are wild, 16.35% planted and 3.95% cultivated species. Majority of the species are found to grow in forest margin, roadside, woodland, wetland and river bank. Most of the species are economically useful as medicine, ornamental and vegetable. This study concludes that the floristic composition of coastal mangrove ecosystems of Barguna district is still rich though the area facing some severe threats. This study strongly recommends adopting effective master plan and implementing adequate measures for sustainable conservation and monitoring of the biodiversity of this disaster-prone area.


Introduction
Taxonomic studies and publications provide basic information of the flora occurring within a specific geographical area, which is essential for plant scientists especially for the plant taxonomists, ecologists, forest managers and planners in understanding and conservation of biodiversity. Irrespective of a small geographical area (147570 km 2 , BBS, 2021), the floristic diversity of Bangladesh is very rich and hosting approximately 5000 species of angiosperms (Khan, 1977). But the floristic exploration throughout this country has not yet been completed during the last five decades after independence of the country, and the floristic compositions in most of the areas of this country are still unknown or poorly understood. A total of about 3886 species have been so far reported from its geographic boundary during the last one and half centuries through sporadically conducted various floristic studies (Hooker, 1872(Hooker, -1897Prain, 1903a, b;Uddin et al., 1998;Khan and Huq, 2001;Rashid and Mia, 2001;Uddin et al., 2003;Siddiqui et al., 2007;Ahmed et al., 2008Ahmed et al., -2009Ahmed et al., 2009;Islam et al., 2009;Arefin et al., 2011;Sultana, 2012;Tabassum, 2015;Haque et al., 2018;Shetu et al., km 2 riverine and 97.18 km 2 under forest (Kamal, 2012, Population and Housing Consensus-2011, 2015. It is intersected by five rivers viz., Baleshwar, Bishkhali, Paira, Haringhata and Khakdon; and 300 natural canals. It has a tropical monsoonal climate with an annual average rainfall of 2,758 mm and annual average temperature of about 25°C (District Statistics 2011 of Barguna, 2013). Soil texture is composed of relative proportions of sand, silt and clay, but maximum area is covered with clay texture (64%) and the rest is clay loam texture (36%). Soils in the south region are both saline and clayey and salinity gradually increases with dryness from January and reached maximum level in the month April-May and decreases due to onset of monsoon rainfall (Population andHousing Consensus-2011, 2015).
The semi-natural and planted coastal mangrove ecosystems of this district are dominated in the sea facing three upazilas including Banguna sadar (4000 acre of Babugonj forest beat under Barguna forest range), Patharghata (3000 acre of Haringhata forest beat under Patharghata forest range) and Taltoli (13634.07 acre of Sakhina and Nishanbaria forest beats under Amtoli forest range) (Fig. 1).
Field surveys were conducted throughout all mangrove ecosystems of Barguna district during different seasons from 2015 to 2022. In this study all mangrove, mangrove associated and nonmangrove species of vascular plants found in wild and as planted or cultivated with their native and exotic origin have been documented. The collection of the vascular plant specimens were conducted following walk through method (Junaid, 2018). The processing, drying and preservation of plant specimens were done following standard herbarium methods and techniques (Bridson and Forman, 1989;Singh and Subramaniam, 2008). The identification of each taxon was done based on its voucher specimens collected by the first and second authors. Taxonomic identification of the specimens and verification of the nomenclatural information has been completed through consulting taxonomic descriptions and keys available in the relevant literatures (Hooker, 1872(Hooker, -1897Prain, 1903a, b;Wu andRaven, 1994-2001;Wu et al., 1999Wu et al., -2013The Plant List, 2013;POWO, 2020;TROPICOS, 2021;Hossain et al., 2021;Khan et al., 2021b;Hossain et al., 2022), and by matching with the respective voucher specimens of DACB and Jahangirnagar University Herbarium (JUH). The families of pteridophytes, gymnosperms and angiosperms have been arranged following the widely used classification systems of Pichi (1977), Kramer and Green (1990) and Cronquist (1988), respectively, whereas the genera and species under each family alphabetically. True mangrove and mangrove associated plant species were recognized following FAO (2007), Giesen et al. (2007) and .
Data on the uses of the species were recorded based on personal experience and also through interviews with the local people which were varifaied through consulting the relevant literature (Siddiqui et al., 2007;Ahmed et al., 2008Ahmed et al., -2009Ahmed et al., 2009;Hossain et al., 2021;Khan et al., 2021a, b;Annon, 2022;Hossain et al., 2022). The rare status of the plant species was inferred through estimation of their current population size, occurrence, distribution range and regeneration in the area based on field observation.

Results and Discussion
This study documents the occurrence of 532 species belonging to 378 genera under 112 families of vascular plants in the mangrove ecosystems of Barguna district, of which 24 (4.51%) species are true and obligatory mangroves, 46 (8.64%) are associates and facultative mangroves and the rest of 461 (86.65%) species are non-mangrove. During this study, Pteridophytes are represented by 22 species under 20 genera of 12 families and Gymnosperms of two species under two genera and families. Among the Angiosperms, dicotyledons are represented by 375 species of 279 genera and 77 families that constituted 70.49% of the vascular flora of the study area, whereas, monocotyledons by 133 species belonging to 77 genera under 21 families, which comprised 25.00% of this flora (Table 1). About 394 species (74.06%) of this vascular flora are native, whereas, 138 species (25.94%) are exotic to Bangladesh.
Pteridaceae and Salviniaceae with four species each representing the largest families of Pteridophyta, which is followed by Polypodiaceae and Thelypteridaceae with three species each. The rest of each families Athyriaceae, Blechnaceae, Lygodiaceae, Marsileaceae, Ophioglossaceae, Psilotaceae, Selaginellaceae and Vittariaceae represented by a single species. The two Gymnosperm families Araucariaceae and Cupressaceae is represented with only one species each. In dicotyledons, Fabaceae with 28 species is recorded as the largest family, which is followed by Asteraceae (with 23 species), Apocynaceae (21 species), Euphorbiaceae (20 species) and Malvaceae (17 species). In monocotyledons, Poaceae is found as the largest family (with 45 species), which is followed by Cyperaceae (31 species), Araceae (15 species) and Arecaceae (10 species). In the study area, a total of 320 (60.15%) plant species are found as herbs that are followed by 116 (21.80%) trees, 84 (15.79%) shrubs, 10 (1.88%) palms and only two (0.38%) bamboos. The most common life-form of this flora is erect herb, which represented 51.56% of the herbaceous species and 31.02% (165 species) of the flora. This life-form was is followed by erect shrubs (70 species), prostrate herbs (56 species), climbing herb (vines) (53 species) and large trees (42 species), comprising 13.16%, 10.53%, 9.96% and 7.89% of this flora, respectively, and medium and small trees representing 7.14% (38 species) and 6.77% (36 species) of the flora. Other lifeforms include creepers, palms, scandent shrubs, rooted floating herbs, epiphytes, submerged and free floating, bamboos, parasitic and lithophytic herbs (Fig. 2). The study area is mostly composed with 394 species (74.06%) of native plants, where one-fourth portion (25.94%) of this flora is formed by 138 exotic species. Most of the flora (424 species) comprising 79.70% are found as wild, whereas 87 (16.35%) species as planted and 21 (3.95%) as cultivated.
The plant species of the study area are found to grow in different habitats including forest margin, roadside, woodland, wetland, river bank, on other plant and brick wall. Among these habitats, most of the species (75.19%) are well-adapted in forest margin, which are followed by 285 (53.57%) species in roadsides, 115 (21.62%) in woodlands, 71 (13.35%) in wetlands, 69 (12.97%) in river banks and 14 (2.63%) species are grown on the branch and trunk of other plants as epiphytes or parasite, whereas only three species are also found to grow on brick walls (Fig. 3). Among the three dominant mangrove ecosystems in Barguna district, a total of 283 (53.20%) species are commonly found in the all these ecosystems, where 491 (92.29%) species are mostly distributed in the Tengragiri reserve forest and Tengragiri wildlife sanctuary which is localy known as Fatrarban. About 396 (74.44%) and 306 (57.52%) species are found to be distributed in Haringhata reserve forest and Padda-Sonbunia-Kumirmara mangrove ecosystems respectively. All species recorded during this study are recognized as economically importance where most of the species (372; 69.92%) are useful as medicine, which are followed by 96 (18.05%) species as ornamentals, 58 (10.90%) as vegetables, 58 (10.90%) as soil binder, 37 (6.95%) as livestock feed 36 (6.77%) as fruits, 30 (5.64%) as timbers and fiber of each and 26 (4.89%) as fuel woods. Additionally, 17 (3.20%) species are useful for green manure and dye yielding of each, 14 (2.63%) as theaching material, 10 (1.88%) as making handicrafts, 9 (1.69%) as hedge plants. A very few number of species are also useful for spice, oil yielding, honey plant, pulse, paper pulp, gum, fish feed, perfume, nut, juice, fish poison, edible and aquarium plant (Fig. 4).
In spite of some severe threats, the study area is still floristically rich than that of previously conducted studies on some coastal ecosystems of the country. The floristic richness of this area might be due to continuous flow of fresh water across the area, its geographical position nearby the world largest mangrove (the Sundarbans) forest, diverse micro-habitats that supports both mangrove and non-mangrove plant species. Besides, the enumeration of the species done in this study is based on the extensive survey and collection throughout all localities of the mangrove ecosystems since a long period of time.
The present study provides baseline information on the vascular flora and revevant threats causing the loss of biodiversity. These information might be useful in undertaking appropriate master plan for sustainable conservation of biodiversity, coastal habitats and socio-economic development of this disaster prone area. The authors highly recommend adopting a master plan for the mitigation of adverse impacts of climate change and anthropogenic interferences. It is strongly suggested to ensure regular monitoring the flora and habitats and implementation of adequate measures for the conservation of rare and threatened plants of this area.