FLORISTIC SURVEY OF VASCULAR PLANTS IN COASTAL DISTRICT BAGERHAT OF BANGLADESH

This survey provides the basic taxonomic data on the vascular flora of the disaster-prone coastal district of Bagerhat. It has explored the occurrence of 964 species of vascular plants under 607 genera and 147 families in this district. About 68.88% of these species are native and 31.12% are exotic to Bangladesh. Pteridophytes are composed of 32 species under 22 genera of 14 families and Gymnosperms of seven species under six genera and five families. Angiosperms are comprised of 693 species of 450 genera and 99 families of Magnoliopsida (dicotyledons) that represent 71.89% of the flora, and 232 species belonging to 129 genera under 29 families of Liliopsida (monocotyledons) that constitute 24.07% of this flora. Fabaceae with 58 species is the largest dicot family, followed by Asteraceae, Euphorbiaceae, Apocynaceae, and Acanthaceae. Poaceae with 68 species is the largest monocot family, followed by Cyperaceae, Orchidaceae, Araceae and Arecaceae. The genus Cyperus is the largest in the study area, which is followed by Fimbristylis , Euphorbia , Ficus , Solanum and Ipomoea . The species Cipadessa baccifera (Roth) Miq. of Meliaceae is rediscovered in Bangladesh. About 63.35% of species of this flora and most of the Magnoliopsida and Liliopsida are herbs, 18.94% shrubs, 15.63% trees, and 1.55% palms. Nearly 70.81% of the species are wild and the rest are planted or cultivated. 17 species are recognized as rare in the study area due to their very restricted occurrence and poor regeneration. Most of the species grow in the fallow lands, roadsides, woodlands, homesteads, marginal lands and scrub jungles. The majority of the species have more than one uses, but most are useful as medicinals (70.39%) and ornamentals (25.57%). Though the study area is under the stress of different threats, its floristic composition is still rich. We strongly recommend adopting adequate effective measures for the conservation and sustainable development of this rich flora of the coastal region .


Introduction
Floristic surveys are essential in understanding the status, extent, and assessment of plant biodiversity (WCMC, 1992). Such surveys are helpful in sustainable utilization of plant resources, plant resource-based development, exploration of alternative and closely allied species, identification and conservation of threatened plant species, and assessment, monitoring and mitigation of the adverse impacts of climate change on plant species. Due to these implications, floristic studies in various forest and non-forest areas become imperative in different areas and countries throughout the world for over a century (Ostertag et al., 2014).
Though it is inferred that Bangladesh houses rich biodiversity including approx. 5000 species of Angiosperms (Khan, 1977), a total of 3886 species are reported from this country through various floristic studies conducted sporadically so far (Hooker, 1872(Hooker, -1897Prain, 1903;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;Rahman et al., 2015;Tabassum, 2015;Haque et al., 2018;Shetu et al., 2018;Uddin and Hassan, 2018;Hossain et al., 2020;Roy and Khan, 2020a, b;Ashrafuzzaman and Sarwar, 2021;Hossain et al., 2021;Khan et al., 2021a, b;Ashrafuzzaman et al., 2022). It indicates that the floristic composition of many areas of this country has been partially explored or unexplored. Besides, Bangladesh is one of the countries that are most vulnerable to climate change and is ranked as one of the world's most disaster-prone areas (Choudhury, 2002;World Bank, 2005) and a good number of plant species in this country are inferred as threatened or under the risk of extinction Ara et al., 2013). Some species with distribution in this country, as reported in old literature (Hooker, 1872(Hooker, -1897 or documented in herbarium collections, may have already been lost. Therefore, conducting adequate floristic surveys in the unexplored or partially explored areas of this country are very crucial to know the composition, structure and status of their plant resources. Today's one of the biggest conservation challenges is to protect and maintain the biodiversity in the coastal areas. The first key step to achieving this goal is to complete the floristic explorations and compile the updated lists of species extant in these areas (Schaminée et al., 2011;Sharrock, 2012). Bagerhat district is a south-western part of the country lying beside the coast of the Bay of Bengal. This district is one of the most risk-prone coastal areas of Bangladesh and most of its habitats and ecosystems are being degraded through the consequences of different natural disasters and anthropogenic interventions, including the replacement of most of its natural vegetation by settlements, agricultural expansions, shrimp cultures and other human activities. But hitherto, this district is floristically unexplored except for its southern part covered with dense forest of Sundarban Mangrove area, the floristic composition of which is largely reported by Rahman et al. (2015). The floristic study of Rahman et al. (2015) covers the mangrove areas of this district belonging to its Mongla-and Sarankhola upazilas but it does not provide information on plant species composition and distribution in other parts of these administrative areas.
The basic taxonomic information on Bagerhat district flora is lacking. In contrast, most of the predominant natural and anthropogenic threats to the flora and plant diversity (Ali, 1999;Choudhury, 2002;Khan, 2008;Kulatunga et al., 2012) are functional throughout this coastal district that can cause a heavy loss of its plant diversity and change in its floristic composition. Therefore, conducting a floristic survey throughout this district is pivotal, especially for knowing the current species composition and diversity, plant resource-based sustainable development, and providing valuable baseline data required for effective conservation of the threatened species and assessment and monitoring of the impacts of anthropogenic climate change on the plants and ecosystems of this area. Therefore, the scope and need for conducting a detailed floristic survey throughout this district are very rationale. This survey was conducted to construct a comprehensive checklist of all vascular plant species extant in the Bagerhat district area and provide basic taxonomic data on these species based on thorough floristic inventories and examination of representative specimens.

Materials and Methods
Bagerhat district, comprising an area of 3959.06 km² including 600.04 km² of forests, is located between 21°49' and 22°59' north latitudes and 89°32' and 89°98' east longitudes (District Statistics 2011of Bagerhat, 2013. It is bounded by Gopalganj and Narail districts on the north, the Bay of Bengal on the south, Gopalganj, Pirojpur and Barguna districts on the east, and Khulna district on the west. This district is composed of nine upazilas (Fig. 1) and 75 unions with a total of 156388 hectares of cultivable lands, 8978 hectares of fallow lands and 9458 hectares of permanently waterlogged areas. The topography of this district is essentially flat, with a maximum elevation change of 36 feet and an average elevation above sea level of 11 feet. It is covered by agricultural lands, fallow lands, grasslands, wetlands and fish ponds ('gher'), scrub jungles, mangrove forests and homestead gardens etc. Bagerhat has a tropical climate with the average annual temperature varying from a minimum of 12.5°C to a maximum of 33.5°C. The rainy period lasts here from February to November but the most rain falls during July, with an average total of 325 mm. The annual average rainfall is 1710 mm (Population andHousing Consensus-2011, 2015).

Map of Bagerhat District
This survey was carried out in different seasons from 2017 to 2022 throughout the Bagerhat district including the Sundarbans area. The collection, processing, drying and preservation of plant specimens were done following standard herbarium methods and techniques (Bridson and Forman, 1989;Singh and Subramaniam, 2008). The representative plant specimens of all taxa were examined at Jahangirnagar University Herbarium (JUH) and Bangladesh National Herbarium (DACB). Taxonomic identification of the specimens and verification of the nomenclatural information has been completed, the families and genera have been arranged, data on the uses of the species have been collected and the status of threatened plant species in the study area has been inferred following Khan et al. (2021b) and Hossain et al. (2021). Most of the voucher specimens are stored at JUH and some at DACB.
Data on the uses of the species were collected through interviews with the local people, and consulting the relevant literature (Ghani, 1998;van Valkenburg and Bunyapraphatsara, 2001;Siddiqui et al., 2007;Ahmed et al., 2008Ahmed et al., -2009. 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 survey reveals the occurrence of a total of 964 species of vascular plants under 607 genera and 147 families within the geographical boundary of the Bagerhat district for the first time. These species constitute about 24.81% of the total 3886 plant species identified (Hossain et al., 2020;Ashrafuzzaman and Sarwar, 2021;Ashrafuzzaman et al., 2022) and 19.28% of the total plant species (Approx. 5000 species) estimated for Bangladesh so far (Khan, 1977).
During this study, Pteridophytes were found to be composed of 32 species under 22 genera of 14 families and Gymnosperms of seven species under six genera and five families. Among the Angiosperms, Magnoliopsida (dicotyledons) were represented by 693 species, including three subspecies and four varieties, of 450 genera and 99 families that constituted 71.89% of the vascular flora of the Bagerhat district, whereas, Liliopsida (monocotyledons) by 232 species, including one subspecies, belonging to 129 genera under 29 families, which comprised 24.07% of this flora (Table 1). About 68.88% (664 species) of this vascular flora are native, whereas, 31.12 % (300 species) are exotic to Bangladesh. Most of the species (618 species), representing 64.11% of this flora, were found to be distributed in the Sundarbans mangrove forests area of this district. In Pteridophyta, Pteridaceae with seven species was the largest, which was followed by Polypodiaceae, Salviniaceae and Thelypteridaceae representing five, four and three species, respectively. Each of the families Marsileaceae, Vittariaceae, and Lygodiaceae was represented by two species. The families representing the Gymnosperms were Cupressaceae and Cycadaceae, each with two species, and Araucariaceae, Pinaceae and Zamiaceae, with only one species each.

Number of species
Life-form category

Floristic composition in different life-form category
Magnoliopsida (472 species) and Liliopsida (181 species) were found in the wild. The rest of the species were recognized as planted (21.53%) and cultivated (7.66%). All species of Pteridophytes were found in the wild but those of the Gymnosperms as planted. The plant species of the Bagerhat district were found to grow in 13 different kinds of habitats (Fig. 3), in which fallow land harbours the higher percentage (30.43%) of species that was followed by roadsides (29.92%), woodlands (22.57%), homesteads (21.22%), marginal lands (20.08%), scrub jungles (14.29%), agricultural fields (13.87%), grasslands (13.66%) and wetlands (10.77%). The occurrence of some species was recorded from gardens, other plants, river banks and brick walls (Fig. 3). The number of species with exclusive distribution in wetlands was 56, in homesteads 36 species, in woodland and on other plants 27 species each, in gardens 23 species, in grassland 21 species, in agricultural fields and roadsides 19 species each, in scrub jungle 14 species, in marginal lands nine species, and in other types of habitats less than four species each.  In Bagerhat, the majority of the species (39.75%) were found to be distributed in all of the nine upazilas. However, Sharankhola, Fakirhat, Bagerhat sadar and Mongla upazilas harboured 29.40%, 25.57 %, 24.95 % and 23.40 % of the species, respectively. The occurrence of a relatively lower percentage of the species was found in other upazilas. A total of 100, 43, 20, and 17 species

Species of different habitats
Species no. Species % were found to be exclusively distributed in Sarankhola, Bagerhat sadar, Fakirhat and Mongla upazilas, respectively. The rest of the upazilas viz., Mollarhat, Kachua, Morelganj, and Rampal, harboured less than three species exclusively, i.e., almost all of the species of these upazilas had overlapping distribution in other upazilas of Bagerhat district (Fig. 4).
Bagerhat district is one of the vulnerable and disaster-prone coastal areas of Bangladesh (Rahman and Ferdous, 2017). Conversion of huge natural and agricultural areas for expanded fisheries projects (Chowdhury and Muniruzzaman, 2003;Karim, 2003;Kabir and Eva, 2014), frequent natural disasters including tidal surges and cyclones, increased urbanization or settlement, construction of highways and railways, unplanned tourism, improper waste management, oil and plastic pollution, increase in salinity and water logging, coal-based power plant establishment, tributary and river bank erosion through increased coastal shipping, invasion of exotic species, and lack of proper management and public awareness etc. are the critical threats for the natural habitats-and ecosystems, flora and species diversity in this district.
Although this district is under the stress of different major threats, its flora is still rich and comparatively in better status than some other districts of the country which might be due to its habitat suitability, landscape structure and continuous flow of fresh water throughout most of its areas through its several major rivers (viz. Panguchi, Daratana, Madhumati, Pasur, Haringhata, Mongla, Baleswar, Bangra and Goshairkhali) and the network of numerous canals, and the occurrence of huge mangrove forests. The data provided by this study on the vascular plants of Bagerhat districts will contribute as the baseline for any further study or development plan involving its biological resources. These data might also be useful to track the trend of changes in the floristic composition, plant species diversity and vegetation in course of time, contribute to the undertaking of appropriate biodiversity conservation initiatives, plant resource-based socioeconomic development, and in the assessment of the impacts of climate change in this region.
To ensure the improvement, conservation and sustainable utilization of the plant resources of the study area, we firmly recommend adopting a master plan for the control and management of the massive anthropogenic interferences and strict enforcement of the forest laws following their necessary updating in this area, implementation of adequate measures for conservation of the threatened and depleting plant species of this area, and strict and adequate management of its protected area. We strongly suggests conducting regular inventories and monitoring programs on the flora and plant diversity of this district. We highly recommend adequate plantation programs, preferably with the wind-and saline tolerant deep-rooted plant species in the coastal belts and the marginal lands of the river-and tributary banks, especially for the mitigation of the adverse impacts of natural disasters and protection of indigenous biological resources of the coastal area.