TAXONOMY OF THE LEAFY VEGETABLES IN BANGLADESH

Thirty four exploration trips made throughout Bangladesh from 2000 to 2012 resulted in identification of 186 taxa used as leafy vegetables in the country, of which 173 taxa belong to angiosperms and 13 taxa to pteridophytes. Among the angiosperms, Magnoliopsida is represented by 153 taxa under 114 genera and 43 families, whereas Liliopsida is represented by 20 species under 15 genera and 8 families. Pteridophytes are symbolized by 13 species belonging to 10 genera and 10 families. Under each taxon updated nomenclature, vernacular names, habit, representative specimen and area of major consumption of the plant as a leafy vegetable have been provided. Out of 186 leafy vegetables identified in Bangladesh, 140 taxa are wild and 46 are cultivated. Among the cultivated ones 16 species are cultivated only as leafy vegetables and 30 are cultivated for other purposes but also used as leafy vegetables. A total of 61 species have been newly documented as leafy vegetables for Bangladesh. Introduction Leafy vegetables are referred to leaves of any plants used as vegetables, sometimes accompanied by tender petioles and shoots. They constitute a major portion of our diet and play an important part in alleviating malnutrition. FAO (2012) has estimated that about 870 million people are chronically undernourished in the period 2010-12 representing 12.5% of the global population, or one in eight people. In order to arrest the undernourished situation, much attention has been paid on the exploitation and utilization of unusual plant materials for food (Kawatra et al., 2001; Dini et al., 2005). Leafy vegetables are important protective foods and highly beneficial for the maintenance of health and prevention of diseases as they contain valuable food ingredients. Usually they have no or very little poisonous alkaloids and do not cause any gastrological disturbance when they are consumed as food. The daily intake of at least 100 g of fresh leafy vegetables is recommended for the adult by nutrition experts (Reddy, 1999). It has been estimated that 100 g of tropical leafy vegetables can provide 60-140 mg of ascorbic acid, 100 mg of folic acid, 4-7 mg of iron and 200-400 mg of calcium (Saxena, 1999). Traditional leafy vegetables are said to be an invaluable substitute for meat and therefore form important part of daily diets of rural communities in particular. Over the last decade many studies have shown that fresh leafy vegetables constitute important functional food components by contributing vitamins, iron, folic acid, minerals, biologically active compounds and photosynthetic pigments (Kmiecik et al., 2001; Su et al., 2002; Kimura and Rodriguez-Amaya, 2003). Traditional leafy vegetables have a proven nutritive value in terms of having more protein, minerals, carbohydrate and vitamins than several common vegetables Institute of Nutrition and Food Science, University of Dhaka, Dhaka 1000, Bangladesh. Corresponding author. Email: dr_oliur@yahoo.com


Introduction
Leafy vegetables are referred to leaves of any plants used as vegetables, sometimes accompanied by tender petioles and shoots.They constitute a major portion of our diet and play an important part in alleviating malnutrition.FAO (2012) has estimated that about 870 million people are chronically undernourished in the period 2010-12 representing 12.5% of the global population, or one in eight people.In order to arrest the undernourished situation, much attention has been paid on the exploitation and utilization of unusual plant materials for food (Kawatra et al., 2001;Dini et al., 2005).Leafy vegetables are important protective foods and highly beneficial for the maintenance of health and prevention of diseases as they contain valuable food ingredients.Usually they have no or very little poisonous alkaloids and do not cause any gastrological disturbance when they are consumed as food.The daily intake of at least 100 g of fresh leafy vegetables is recommended for the adult by nutrition experts (Reddy, 1999).It has been estimated that 100 g of tropical leafy vegetables can provide 60-140 mg of ascorbic acid, 100 mg of folic acid, 4-7 mg of iron and 200-400 mg of calcium (Saxena, 1999).Traditional leafy vegetables are said to be an invaluable substitute for meat and therefore form important part of daily diets of rural communities in particular.
Over the last decade many studies have shown that fresh leafy vegetables constitute important functional food components by contributing vitamins, iron, folic acid, minerals, biologically active compounds and photosynthetic pigments (Kmiecik et al., 2001;Su et al., 2002;Kimura and Rodriguez-Amaya, 2003).Traditional leafy vegetables have a proven nutritive value in terms of having more protein, minerals, carbohydrate and vitamins than several common vegetables (Sundriyal and Sundriyal, 2001;Fasuyi, 2006;Orech et al., 2007).Leafy vegetables also contain antioxidants which offer protection against many chronic diseases including heart disease and certain types of cancer (Saxena, 1999).
In Bangladesh, people have a long heritage of taking leafy vegetables.However, very little attempt has been made to study the leafy vegetables of Bangladesh although they constitute a large proportion of the daily diet of the rural dweller of the country (Ali et al., 1977;Sarker and Hossain 2009;Hassan, 2010).Despite the importance of leafy vegetables in the present day human lives, no systematic work has been carried out in Bangladesh to identify and document the plant species.In view of potential beneficial attributes of leafy vegetables, there is a need to explore, identify and document the leafy vegetables of the country.The objectives of the present study are therefore three-fold: i) to make an inventory, and identify the leafy vegetables, ii) to document the leafy vegetables including wild and cultivated ones, and iii) to carry out a detailed systematic study on the leafy vegetables of Bangladesh.

Results and Discussion
A total of 186 leafy vegetable taxa have been identified in Bangladesh of which 173 belong to angiosperms, and 13 to pteridophytes.Among the angiospermic taxa Magnoliopsida is represented by 153 and Liliopsida is represented by 20 taxa (Table 1).The taxonomic enumeration of the leafy vegetables is briefly described below.

Thelypteridaceae
Taxonomic study on the leafy vegetables is the first in its nature in Bangladesh.The present study shows that Amaranthaceae is the largest family in Magnoliopsida represented by 14 species followed by Asteraceae, Cucurbitaceae and Fabaceae comprising 10 species each.In Liliopsida, Araceae stands the highest position with 9 species followed by Zingiberaceae with 3 species.Out of 10 families of pteridophytes the families Athyriaceae, Marsileaceae and Parkeriaceae possess 2 species each.Twenty seven familes are represented by a single species used as leafy vegetables of which 20 families belong to angiosperms and 7 families to pteridophytes.Fifteen largest families of leafy vegetables reported to be found in Bangladesh are shown in Fig. 1.The study reveals the identification of 61 newly documented leafy vegetables for Bangladesh (Table 2).The majority of these newly documented leafy vegetables are consumed by the people of the hilly areas, especially in the Chittagong Hill Tracts and greater Sylhet district.
Out of 186 leafy vegetables recorded for Bangladesh, 140 taxa are wild and 46 are cultivated.Among the cultivated ones, 16 taxa are cultivated only for leafy vegetables, viz., Amaranthus tricolor, A. viridis, Basella alba, Benincasa hispida, Brassica oleracea var.Indigenous leafy vegetables can play an important role to alleviate hunger and malnutrition, but they are often neglected in research.They are important sources of micronutrients including Vitamin A and C, iron and other nutrients and are sometimes better nutritional sources than the modern vegetables.Wild leafy vegetables do not warrant any health hazard as they are free from any insecticide, herbicide and pesticides as well as free from the application of chemical fertilizers.Therefore, wild leafy vegetables are superior to the cultivated ones, if they are more or less similar in nutritional values.Despite leafy vegetables have continuously been neglected for long time by the elite people, specially of urban societies, and has been referred to as "Shak, the poor men's food", now with the advancement of scientific research on their nutritive and medicinal values, have become an important item of our daily diet.Edible plants are thought not to contain any risk factors, therefore research for wild edible plants is necessary specially for famine situation and for the people living in rural and forest areas.
The present study on the leafy vegetables of Bangladesh is the most comprehensive study in the country.Extensive botanical exploration throughout the country over ten years resulted in documentation of 61 new reports as leafy vegetables for Bangladesh presenting 30.8% new addition to the species used as leafy vegetables.This provides a baseline study that could through more light on further research, particularly on nutra-medicinal aspects including determination of proximate nutrients, vitamins, micronutrients, macronutrients.Considring the present study as a baseline, if the nutrient compositions and other nutra-medicinal properties (i.e.antidiabetic, anticancerous, antibacterial and antioxidant) of the leafy vegetables, particularly the newly documented species could be determined, it would be possible to alleviate poverty and malnutrition in Bangladesh through the increased production and consumption of nutritious and health-promoting leafy vegetables.