ANGIOSPERMS IN NARSINGDI DISTRICT OF BANGLADESH: CLASS MAGNOLIOPSIDA

This study presents taxonomic information on 468 plant species belonging to 326 genera and 85 families of the angiospermic class Magnoliopsida (dicotyledones) from Narsingdi district of Bangladesh. In this area, Fabaceae with 53 species of 37 genera is the largest family, followed by Asteraceae with 25 species of 24 genera and Rubiaceae with 21 species of 17 genera. Ficus with eight species is appeared as the largest genus, which is followed by Persicaria and Solanum with seven species each, Lindernia with six species, Phyllanthus with five species, and Acacia, Amaranthus, Senna, Sida and Trichosanthes with four species each. Herbs are comprised of 230 (49.14%) species that are followed by trees of 120 (25.64%) species, and shrubs of 118 (25.21%) species. The similarity measured by Jaccard coefficient shows that the six upazilas of Narsingdi district are relatively more similar (75.47%) in their species composition if they are compared all together. However, the similarities vary from 9.03% to 50% if only two upazilas are compared. In this district, total 333 species have been distinguished as economically useful. The species Rauvolfia serpentina of Apocynaceae, Geophila repens of Rubiaceae and Acmella radicans of Asteraceae have been assessed as Endangered (E) in this district. Introduction Bangladesh constitutes a significant part of the South Asian Mega Centre of genetic diversity (Chowdhury, 1996), and supports a rich biodiversity including a huge number (approx. 5000) of Angiosperm species (Khan, 1977). However, Angiosperms of many areas of this country have so far been poorly or partially explored or unexplored. Therefore, performing taxonomic studies in these areas is essential to know the status of plant resources of this country. Narsingdi is one of the central districts of Bangladesh, located at 50 km northeast of the capital city Dhaka. Some of the previous floristic studies cover the area of the present political boundary of Bangladesh (Prain, 1903; Hooker, 1872-1897; Ahmed et al., 2008-2009). Many other studies were conducted in the different areas of this country (Rahman and Hassan, 1995; Rashid, et al., 1995; Rashid and Mia, 2001; Khan and Huq 2001; Alam et al. 2006; Islam et al. 2009; Tutul et al. 2010; Arefin et al. 2011; Rahman et al. 2012; Rahman, 2013; Sarker et al. 2013; Rahman et al. 2015; Haque et al., 2016, 2018; Shetu et al. 2018). However, the flora and plant diversity of Narsingdi district have not yet been studied based on field inventories and examination of plant specimens. Moreover, this district is also one of the most risk prone areas of Bangladesh because most of its areas harboring the natural vegetation are continuousely being replaced by urbanization with numerous infrastructures, industrialization, habitat fragmentation, agricultural expansion and other human interventions. Therefore, there is a great need for conducting a detail floristic study throughout this district. *Corresponding author, email: robaydakhanam@yahoo.com


Introduction
Bangladesh constitutes a significant part of the South Asian Mega Centre of genetic diversity (Chowdhury, 1996), and supports a rich biodiversity including a huge number (approx. 5000) of Angiosperm species (Khan, 1977). However, Angiosperms of many areas of this country have so far been poorly or partially explored or unexplored. Therefore, performing taxonomic studies in these areas is essential to know the status of plant resources of this country.
Narsingdi is one of the central districts of Bangladesh, located at 50 km northeast of the capital city Dhaka. Some of the previous floristic studies cover the area of the present political boundary of Bangladesh (Prain, 1903;Hooker, 1872Hooker, -1897Ahmed et al., 2008Ahmed et al., -2009. Many other studies were conducted in the different areas of this country (Rahman and Hassan, 1995;Rashid, et al., 1995;Rashid and Mia, 2001;Khan and Huq 2001;Alam et al. 2006;Islam et al. 2009;Tutul et al. 2010;Arefin et al. 2011;Rahman et al. 2012;Rahman, 2013;Sarker et al. 2013;Rahman et al. 2015;Haque et al., 2016Haque et al., , 2018Shetu et al. 2018). However, the flora and plant diversity of Narsingdi district have not yet been studied based on field inventories and examination of plant specimens. Moreover, this district is also one of the most risk prone areas of Bangladesh because most of its areas harboring the natural vegetation are continuousely being replaced by urbanization with numerous infrastructures, industrialization, habitat fragmentation, agricultural expansion and other human interventions. Therefore, there is a great need for conducting a detail floristic study throughout this district.
This study has been carried out to construct a taxonomic checklist of the angiosperms under the class Magnoliopsida (dicotyledones) of Narsingdi district based on thorough taxonomic inventories throughout the area to serve as a taxonomic baseline on the current status of the species of this plant group in this area, contribute in further studies on the change in floristic composition, plant species diversity and vegetation, help in adopting appropriate biodiversity conservation initiatives and promote plant resourse-based socioeconomic development projects in this area. then their sequence turns in to Belabo, followed by Palash, Monohordi, Shibpur, Narsingdi Sadar, and Raipura. According to Jaccard coefficient, the similarity in six upazilas of Narsingdi district in harboring the dicotyledonous species was 75.47% (Fig. 1). It indicates that the species composition in these upazilas are more similar rather than different if they are compared all together. However, the similarities in between the two upazilas only varied from 9.03% (in Monohordi and Raipura upazilas) to 50% (in Monohordi and Belabo upazilas). Fig. 1. Similarity in species composition in the upazilas of Narsingdi district based on Jaccard coefficient (Jaccard, 1912).
These rercords on dicotyledonous species of six upazilas of Narsindi district are higher than the enumeration of this plant group in some upazilas of other districts by the previous studies, (Islam et al., 2009;Rahman et al., 2012;Sarker et al., 2013;Sajib et al., 2014;Mahmudah et al., 2017;Rahman et al., 2019). Whereas, the record on dicot species of Raipura upazila by this study is somewhat lower than that of Munshiganj Sadar upazila by Rahman et al., 2013, though those of other upazilas of Narsindi district are notably higher. Considering the size of the study area, the dicotyledonous flora of whole Narsingdi district seems richer in comparison to those of Sundarbans, Patuakhali district and Rajshahi district, as reported by Rahman et al. (2017), Sultana (2012) and Rahman (2013), respectively. Whereas, the dicotyledones of this district is relatively poorer than those of few forest areas viz., Sitapahar Reserve Forest (Uddin et al., 1998;Rashid and Chowdhury, 2013), Satchari National Park (Arefin et al., 2011); Hazarikhil Wildlife Sanctuary (Rahman, 2017), and Rajkandi Reserve Forest (Haque et al., 2018). These variation in species composition of different areas might be due to different natural, biogeographical and anthropogenic factors, drivers or threats etc. functioning in these area, and the methods and intenseness of the studies as well.
During this study, total 333 dicot species of Narsingdi district were figured out as economically useful. The major categories of these species were medicinal (167 species), timber (46 species), fruit (37 species), ornamental (60 species), vegetable (43 species), fodder (9 species), fiber (11 species), fuel wood (12 species), oil yielding (five species), pulse (four species) and spices (three species). Among these species, 67 were recognized to be useful in two to three categories. The total number of dicot species (468) recorded from Narsingdi district during this study was 17.84% of the total 2623 species, and the number of dicot families (89) was 56.32% of the total 158 families reported for Bangladesh by Ahmed et al. (2008Ahmed et al. ( -2009. However, these proportions of the dicots of this district would be decreased if the flora of Bangladesh is explored completely. One threatened species Rauvolfia serpentina (L.) Benth. ex Kurz found in the study area is already included in Red Data Book of Vascular Plants of Bangladesh . The species Geophila repens (L.) I.M. Johnst., rediscovered (Khanam et al., 2018) from this area, wasis found as threatened there, which is not yet included in the Red Data Book of Vascular Plants of Bangladesh. In the study area, the populations of Geophila repens (L.) I. M. Johnst. and Rauvolfia serpentina (L.) Benth. ex Kurz were comprised of total 50 and nine individuals, respectively. G. repens and R. serpentina were confined to two and four localities with the Extent of Occurrence (EOO) and Area of Occupancy (AOO) of 250 km 2 and 25 km 2 , and 280 km 2 and 50 km 2 , respectively. Another species Acmella radicans (Jacq.) R.K. Jansen was found in five localities of Shibpur upazila with total 40 individuals only. Its EOO and AOO were estimated as 120 km 2 and 15 km 2 , respectively. The regeneration in these three species was poor and their localities were under the regular stress of habitat destruction due to which these species have been considered as Endangered (E) in Narsingdi district. Both of Acmella radicans and Geophila repens might be included in the Red Data Book of Vascular Plants of Bangladesh and IUCN Red List for Bangladesh following exploration in other areas of this country. Different anthropogenic activities continuously performed by increased human population, especially vegetation clearing, unnecessary firing, unplanned agricultural extension, over exploitation of natural resources, and habitat fragmentation and depletion; soil erosion; invasion of some exotic species (e.g. Acacia auriculiformis, Chromolaena odorata, Eucalyptus camaldulensis, Mikania cordata and Parthenium hysterophorus); poor regeneration in some species; lack of awareness in the local people; and lack of proper management programs etc. are the major functional threats to the flora of the study area.
The taxonomic information provided by this study on the species of dicotyledons extant in Narsingdi district can serve as an important guiding database to track the trend of changes in the floristic composition, plant species diversity and vegetation in course of time due to natural and anthropogenic stresses, contribute in undertaking appropriate biodiversity conservation initiatives and plant resourse-based socioeconomic development and help in estimating the impacts of climate change in this area. This study highly recommends for regular inventory, monitoring and specific research programs on the flora and plant diversity of this district and implementation of appropriate conservation measures for the threatened and depleting plant species of this area.