AN ANNOTATED CHECKLIST OF THE VASCULAR PLANTS OF SUNDARBAN MANGROVE FOREST OF BANGLADESH

The study revealed the occurrence of 528 species of vascular plants belonging to 356 genera and 111 families in the Sundarban Mangrove Forest of Bangladesh. Among these species, 24 were pteridophytes and the rest were angiosperms, of which only 24 were true mangroves and 70 were mangrove associates. Magnoliopsida and Liliopsida were represented by 373 and 131 species, respectively. These species belonged to 345 herbs, 89 shrubs and 94 trees. Sixty-four species were climbers, 14 were epiphytes, 6 were parasites, and 7 were palms. The species number per family varied from 1 to 42. In pteridophytes, Pteridaceae with 4 genera and 5 species was the largest family. In angiosperms, Fabaceae with 24 genera and 42 species and Poaceae with 27 genera and 42 species were the largest families, respectively, in Magnoliopsida and Liliopsida. Most of the species included in this checklist were found in oligohaline zone, Sarankhola range and the forest margins, and recognized as economically important. Eleven species categorized as threatened in Bangladesh were found to occur in this mangrove forest. Introduction The Sundarban, located in south of the Tropic of Cancer at the northern limits of the Bay of Bengal and covering a vast area of about 10,029 sq km in the territory of Bangladesh and India (Hussain and Acharya, 1994), is the world’s largest single chunk of productive mangrove forest ecosystems (Das and Siddiqi, 1985). The major part (62%) of this mangrove forest belongs to Bangladesh. Sundarban Mangrove Forest of Bangladesh (SMFB) is remarkably important for its floristic and faunal composition, wildlife habitats, and ecological values due to which it was declared as the world’s 560th Ramsar Wetlands Site in 1992 and the 798th World Heritage Site by the UNESCO in 1999 (Nishorgo, 2008; Hossain et al., 2015). The Sundarban is a unique ecosystem in the world (Biswas et al., 2007) and one of the biodiversity rich sites in Bangladesh (Prain, 1903). The forest of Bangladesh Sundarban is serving as a natural barrier against different natural calamities, like storms, cyclones and tidal bores for a large part of coastal settlements. The SMFB has drawn attention of the people through different socio-economic contributions to this country, especially supporting many industries, local economy and communities by supplying various raw materials, and its fantastic natural beauty. Floristic composition of this mangrove forest is considered as very rich compared to other mangroves in the world due to its geo-physical location near the Indo-Burma global prime hotspot region (Mittermeier et al., 1998). Before and after Prain (1903), nobody, however, is known to conduct a detailed floristic study on the vascular plants surveying most of the areas of this mangrove that harbours diverse wildlife and parts of which are usually inaccessible due to very adverse weather in summer and monsoon. Corresponding author. Email: sayedur27bcs@gmail.com Bangladesh National Herbarium, Chiriakhana Road, Mirpur 1, Dhaka 1216, Bangladesh


Introduction
The Sundarban, located in south of the Tropic of Cancer at the northern limits of the Bay of Bengal and covering a vast area of about 10,029 sq km in the territory of Bangladesh and India (Hussain and Acharya, 1994), is the world's largest single chunk of productive mangrove forest ecosystems (Das and Siddiqi, 1985).The major part (62%) of this mangrove forest belongs to Bangladesh.Sundarban Mangrove Forest of Bangladesh (SMFB) is remarkably important for its floristic and faunal composition, wildlife habitats, and ecological values due to which it was declared as the world's 560th Ramsar Wetlands Site in 1992 and the 798th World Heritage Site by the UNESCO in 1999(Nishorgo, 2008;Hossain et al., 2015).
The Sundarban is a unique ecosystem in the world (Biswas et al., 2007) and one of the biodiversity rich sites in Bangladesh (Prain, 1903).The forest of Bangladesh Sundarban is serving as a natural barrier against different natural calamities, like storms, cyclones and tidal bores for a large part of coastal settlements.The SMFB has drawn attention of the people through different socio-economic contributions to this country, especially supporting many industries, local economy and communities by supplying various raw materials, and its fantastic natural beauty.Floristic composition of this mangrove forest is considered as very rich compared to other mangroves in the world due to its geo-physical location near the Indo-Burma global prime hotspot region (Mittermeier et al., 1998).
Before and after Prain (1903), nobody, however, is known to conduct a detailed floristic study on the vascular plants surveying most of the areas of this mangrove that harbours diverse wildlife and parts of which are usually inaccessible due to very adverse weather in summer and monsoon.Hooker (1872Hooker ( −1897) ) studied the flora of the then British India including many areas that belong to the present political boundary of Bangladesh.Prain (1903) for the first time studied the flora of both Indian and Bangladesh Sundarban concurrently.After that, a small part of the flora or plant diversity of this mangrove was inventoried sporadically without providing information on plant specimens examined (e.g.Chapman, 1976;Chaffey et al., 1985;Das and Siddiqi, 1985;Karim, 1994;Rashid et al., 2008;Islam et al., 2014).Rahman et al. (2012Rahman et al. ( , 2014) ) and Hossain et al. (2015) studied particular plant groups of this mangrove providing the lists of specimens examined.
Since no complete floristic study was carried out throughout the SMFB after Prain (1903), it is completely unknown if any change in the floristic composition of this mangrove has occurred over the last more than one hundred years.On the other hand, the SMFB belongs to one of the world's most risk-prone areas where the plant diversity is increasingly being depleted due to overextraction and destruction of natural resources, and on-going and predicted adverse impacts of climate change (Hussain, 2014).Therefore, there is a great need for conducting a detail floristic study throughout this mangrove forest.In the present study, an annotated checklist of vascular plant species of the SMFB has been constructed based on a thorough taxonomic inventory conducted throughout the area and examination of the representative plant specimens to provide the updated information on the floristic composition and distribution in the SMFB and a way of focusing and stimulating further work in this mangrove forest.

Materials and Methods
The SMFB lies between the latitudes 21°30′N and 22°30′N and longitudes 89°00′E and 89°55′E (Hussain and Acharya, 1994;Hoq, 2008).The total area of SMFB is about 6,017 sq km that is composed of the landmass of 4,143 sq km (Katebi, 2001) and water bodies of 1,874 sq km in the forms of complex network of rivers, canals and tidal creeks (Iftekhar and Islam, 2004).It consists of about 4.07% of total land mass of the country and 40% of total forest land (BFD, 2015).
This study, conducted during 2010−2014, was based on a thorough taxonomic inventory on wild, planted and cultivated vascular plants growing in the SMFB.A total of 3,103 representative specimens were collected during 15 extensive field trips, each consisted of 12−15 days, covering all types of forests and habitats of most of the areas throughout the SMFB (Fig. 1).These specimens were carefully examined in Plant Systematics and Biodiversity Laboratory of Jahangirnagar University and Bangladesh National Herbarium (DACB), Dhaka.The freshly collected specimens were properly processed and managed using standard herbarium techniques (Hyland, 1972;Jain and Raw, 1977) and deposited at Jahangirnagar University Herbarium (JUH).Besides, the first and second authors' own collections and the herbarium specimens previousely collected from the same area by different collectors and deposited at the JUH and the DACB were also examined.

Results and Discussion
The study revealed the occurrence of 528 species belonging to 356 genera under 111 families of vascular plants in the SMFB.Among the species enumerated, 504 (95.46%) were angiosperms and the rest 24 (4.54%) were pteridophytes (Table 1).Twenty-four species were true mangroves, 70 were mangrove associates and 434 were non-mangrove species (Table 2).Thirty-two species of mangrove associates and all non-mangrove species included in this checklist were previousely reported from the Bangladesh territory (Siddiqui et al., 2007(Siddiqui et al., −2008;;Ahmed et al., 2008Ahmed et al., −2009)).In this study, 48 families were found as monogeneric and monospecific and only 15 families were found to be comprised of 10−42 species.Pteridaceae with five species was found as the largest family of Pteridophyta in the SMFB followed by Polypodiaceae with four species and Salviniaceae with three species.Fabaceae with 42 species was recorded as the largest dicotyledonous family in the SMFB followed by Euphorbiaceae with 29 species and Asteraceae with 27 species.In monocotyledons, Poaceae was the largest family with 42 species followed by Cyperaceae with 39 species and Orchidaceae with 9 species.The specimen Sayedur18 (JUH) of Pteridophyta and Sayedur551 (JUH) of Magnoliopsida are recognized here as dubious taxa.
In the SMFB, 345 species (65.34%) were found as herb followed by trees (94 species or 17.80%) and shrubs (89 species or 16.86%).A total of 251 species were found to be distributed exclusively in oligohaline zone, 103 species in mesohaline zone, 57 species in polyhaline zone, and 120 species in more than one saline zone.Sarankhola Forest Range haboured 447 species, Khulna Range 250 species, Chandpai Range 151 species, Satkhira Range 130 species, and 108 species were found in all four forest ranges of the SMFB.
Throughout the SMFB, the forest margins were found as the most common habitat harbouring a total of 255 species, of which 47 were planted and six were cultivated.All of the planted and cultivated species were found to grow only on the uninundated areas and some of these species were found to be naturalized there (e.g.Acacia nilotica (L.) Willd.ex Delile, Pithecellobium dulce (Roxb.)Benth.and Syzygium cumini (L.) Skeels).The genus Colubrina Rich.ex Brongn.and its species C. javanica Miq. of family Rhamnaceae were recently reported as new angiosperm records for Bangladesh (Rahman et al., 2014).Most of the species found in the SMFB are economically important, especially as sources of timber, fuel wood, fruits and vegetables, and also as fodders, medicinal plants, ornamental plants and soil binders.A large number of species were recorded as weeds (Fig. 2).
The number of plant species recorded for the SMFB by the previous studies conducted after Prain (1903) was much lower (e.g.65 and 48 species of true mangroves, mangrove associates and non-mangroves, respectively, by Chaffy et al., 1985 andRashid et al., 2008) than that of the present study.The consideration of a number of quadrat sampling plots on selected areas (Chaffy et al., 1985;Rashid et al., 2008) or only a particular plant groups (e.g.undergrowths by Rashid et al., 2008) in those studies might be the potential reasons for this notable differences in the findings.In comparison with the species composition of other forests of Bangladesh (e.g.Uddin et al., 1998;Uddin and Hassan, 2004), the total number of species found in SMFB seems to be lower in respect to its area.Impacts of salinity, water logging, tidal action, poor humus, and natural disaster on the SMFB might be the reasons for comparatively lower species richness (Chowdhury, 2001).
The present checklist is an attempt to list down all vascular plant species currently occurring in the SMFB, thus updating our floristic knowledge of this unique ecosystem.It can be considered as an important database as well as baseline to track changes in the floristic composition of the SMFB in course of time, especially in the light of the introduction of new species and/or loss of the current species as a result of different biogeographical processes or risks, especially by multifarious anthropogenic activities and different natural hazards operating there.This checklist may further stimulate research and management in the SMFB by serving as a valuable 'snapshot' of the flora of this globally important mangrove.

Fig. 1 .
Fig.1.Map of the Sundarban Mangrove Forest of Bangladesh (SMFB) showing specimen collection sites

Fig. 2 .
Fig.2.Economic categories of vascular plant species found in Sundarban Mangrove Forest of Bangladesh (SMFB).Several species had more than one economic uses.

Table 2 . List of vascular plants of the Sundarban Mangrove Forest of Bangladesh.
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