Taxonomic diversity of broad-leaf weeds at Bangladesh Agricultural University campus and their ethnobotanical uses Most

An intensive survey and literature review was furnished to study taxonomic diversity and ethnobotanical uses of broad-leaf weeds available in BAU campus. Availability of 107 broad-leaf weed species has been identified and those belong to 78 genera and 38 families. Among the families, Fabaceae is best-represented with 13 weed species followed by Euphorbiaceae and Amaranthaceae (seven species in each), Solanaceae (six species), Convolvulaceae and Polygonaceae (five species); 17 families are represented by two to four species while 15 families by single species in each. The genera viz. Desmodium, Ludwigia and Solanum, are represented by four species in each followed by Amaranthus, Ipomoea, Lindernia, Persicaria and Senna three species in each; however, most of the genera are represented by one or two species in each. Three distinct phenology (flowering periods) viz. October-March (52), April-September (40) and all the year-round (15), were observed among identified weed species and the knowledge on phonological development would be helpful to know soil seedbank potential for their effective management. These weed species possess many ethnobotanical uses e.g., medicinal value, consumed as vegetable, feed, fodder, etc. This study provides information on ethno-botanic uses, taxonomic diversities and phenology of the broad-leaf weeds for their effective management. Article history: Received: 16 October 2019 Accepted: 19 November 2019 Published: 31 December 2019


Introduction
Weeds are unwanted and undesirable plants which interfere with the utilization of land and water resources and thus adversely affect human welfare (Rao, 2000). About 1570 plant species are recognized as weeds (absolute weed) throughout the world (Wiersema and Leon, 1999) and about 350 species of weeds are recorded from the crop fields of Bangladesh. About 20% of the present weed flora have been recognized as naturalized exotic weeds e.g., Argemone maxicana, Alternanthera philoxeroides, Clerodendrum viscosum, Croton bonplandianum, Lathyrus aphaca, Lantana camara, Mimosa pudica, Nicotiana plumbaginifolia, Urenia lobata, Vicia angustifolia, etc. (Hossain and Pasha, 2004). Uncontrolled weed growth, especially in the early stages of crop establishment, causes yield loss up to 25-80% depending upon types of crops (Kashem et al., 2009); and the global economic losses more than $40 billion per annum occurs due to weeds through reduction of agricultural and silvicultural productivity, reduced access to land and water, impaired aesthetics and disruption of human activities and well-being (Kashem et al., 2009). Despite these negative effects, weeds act as ground cover, source of organic matter and genetic materials for crop improvement, nutrient cycling, and possess many ethno-botanical uses e.g., medicine, vegetable, feed and fodder for domestic animal, etc. Not only in the Indian subcontinent and its neighbourhoods, weed species are also used for medicinal purposes in other regions of the world, for example Highland Maya of Chiapas (Mexico) and North American regions; weeds used in traditional medicinal floras may be the source of important new drugs (Stepp and Moerman, 2001).
An effective management (/control) program is essential to reduce the crop yield losses due to weeds. Weed management is a better option than control due to reduce crop production cost, protect natural balance, conserve environment, avoid elimination of species, avoid injury of main crops, encourage beneficial effects, and increase production. The knowledge on weed morphology and identification, habitat, viability and dormancy of weed seed, competitive ability with crop, etc., is essential to achieve an effective management program (Kashem et al., 2009). In Bangladesh, the detailed taxonomic studies including phenology of weeds have been neglected by both the practising plant taxonomists and/or the agricultural scientists. We have scanty information on the weeds of different crops in agronomic publications (Islam, 2014;Akter et al., 2018;Shabi et al., 2018). The Bangladesh Agricultural University (BAU) campus with three major topographic types viz. plain area, slightly undulated area and basin-shaped low lying area, facilitates a wide range of habitats such as wetlands, marshy lands, open fields, fallow lands, etc. (Sarwar and Prodhan, 2011). The mean annual rainfall is 244.15 mm and the temperature varies from 11.9º to 32.5º C. This diverse climatic condition and wide habitat range provide a suitable condition for the growth of weeds in this campus which harbours a wide range of plant diversities. To make a complete weed flora of BAU campus, an intensive taxonomic study on the weeds available in this campus has recently been started (Cyperaceae, Jannat-E-Tajkia et al., 2018;Poaceae, Sagar et al., 2018;Asteraceae, Mia et al., 2019). As a part of this research, the species diversity of (dicotyledonous) broad-leaf weeds including their habitat, flowering period and ethno-botanical uses, have been reported here which might be useful for the green weed management practices and for getting higher economic benefits.

Results and Discussion
An enumeration of the species recorded was presented with botanical name, common name(s), English name, family, flowering time and habitat. In this present paper, the occurrence of 107 weed species belong to 78 genera and 38 families has been reported (Tables 1 and 2). One weed species could only be identified down to genus level (Phyllanthus sp.). Among the families, Fabaceae is the best-represented family with 13 species followed by Euphorbiaceae and Amaranthaceae (Seven species in each), Solanaceae (six species). Convolvulaceae and Polygonaceae are represented by five species each; 17 families are represented by two to four species in each while 15 families by a single species in each (Table 2). Among the genera, the largest genera are Desmodium, Ludwigia and Solanum represented by 4 species each followed by Amaranthus, Ipomoea, Lindernia, Persicaria and Senna by 3 species each; however, most of the genera are represented by single or two species each (Table 1). The distribution pattern of weeds (number of genera and/or species) was varied from place to place. For example, the number of weed species belongs to the family Fabaceae varies from 6 to 14 (Mamun, 1989;Moody, 1989;Karim and Kabir, 1995;Khan and Parveen, 2018). Looking through the weed flora of the BAU campus, Poaceae was the largest family (81 species) followed by Cyperaceae (48 species) and Asteraceae (26 species); moreover, Fimbristylis (13 species) and Cyperus (12 species) of the family Cyperaceae were most species-rich genera followed by Digitaria (9 species) of the Poaceae (Jannat-E- Sagar et al., 2018;Mia et al., 2019). Apart from the Poaceae, many of the top 12 weed families are also the same families that are important for medicinal viz.
Some of these recorded weed species are common and major weeds in the rice, wheat, jute and other crop fields (Islam, 2014;Akter et al., 2018;Shabi et al., 2018). Species from the genera Lantana, Amaranthus, Cassia, Cephalandra, Anisomeles, Cleome, Croton, Desmodium, Dryopteris, Justicia, Mimosa, Melochia, Oxalis, Scoparia, etc., were very common and distributed all over the habitat (campus). The habitat diversity varied from crop fields and its levees to roadsides, fallow lands, play grounds, waste lands, edges of drains, dry lands, shallow water bodies, etc. Based on the phenology (flowering times), identified weed species belong to three distinct groups i.e., flowering occurs during the month of October-March (52 species), April-September (40 species) and all the year-round (15 species) ( Table  1). The knowledge of habitats and flowering period can be utilized as an effective tool for the management of weeds. Appropriate management practices before/at flowering will help us to maintain the weed population below the economic threshold level and break-up the weed seedbank in the soil for future regeneration. It is, therefore, essential to understand the phenology and habitat of the weeds to select the appropriate management practices. Hence, the population of weeds can be maintained below the economic threshold level if these weeds can be managed before flowering. Weeds, at the field margins and the surrounding natural vegetation, sometimes provide a habitat where beneficial arthropods may find refuge, alternative hosts, water, overwintering sites, favourable microclimate and escape from pesticides applied to the crop.
Weeds, regarded undesired in crop field and neglected as the constant source of annoyance and trouble to the farmers, are simply eradicated by mechanical and/or chemical means; though they are important from the standpoint of medicinal, allelopathic and food values (Bhattacharjya and Borah, 2008). Ethnic/tribal peoples have been consuming these weeds for generations not only as medicine but as food also. The study reveals that the weeds from the crop fields and wastelands possess multiple medicinal uses. The ethno-botanical uses of the reported weeds are much diversified (Table 3) and also recorded in different ethno-botanical references (Uddin, 2006). Out of 107 weed species, a total of 69 species have the medicinal properties/uses while 26 species used both as vegetable and medicinal purposes, three species as vegetable, one as fodder crop, one as fodder and medicine, one species is used as fish poison. Hitherto, six species did not have any known ethno-botanical uses (Table 3). Recent time, there are a lot of difficulties to collect medicinal plants from forest due to Government's forest policies. Therefore, the crop fields and other disturbed ecosystems are preferred habitats for medicinal plant collection and/or procurement by many traditional peoples (Immanuel and Elizabeth, 2009). Weeds in disturbed areas are likely to have more chemicals in them for defense which are biologically active and potentially useful for medical science. Out of the various parts used as native medicines, leaf and shoot or the whole plant is commonly used; roots, buds, flowers, fruits, seeds and exudates like latex and juices are less commonly used (Panda and Misra, 2011). These medicinal plants are commonly used by the local people to cure following the diseases viz. fever, asthma, urinary problems, cough, cold, small pox, dysentery, diarrhoea, diabetes, eczema, fracture of bone, headache, heart disease, itches, jaundice, menstrual disease, paralysis, piles, skin diseases, snake-bite, toothache, vomiting, worm, wound and others (Table 3).
Based on medicinal uses, species from the genera namely Anisomeles, Chenopodium, Coccinia, Colocasia, Croton, Cuscuta, Desmodium, Eichhornia, Euphorbia, Heliotropium, Indigofera, Ipomoea, Justicia, Lantana, Lippia, Mimosa, Oldenlandia, Phyla, Portulaca, Senna, Sida and Solanum have diversified ethno-medicinal uses. A single weed species is sometimes used for the treatment of many diseases. For example, Colocasia esculenta is used to treat jaundice, cut & wounds, antibacterial & hypotensive, menstruation, stomach problems, cysts, poultice to boils, conjunctivitis, constipation, colic, digestive; Mimosa pudica to treat dysentery, haemorrhoids, mouth ulcer, sore nipples, scurvy, disease of kidney, liver, spleen bladder, pyorrhoea, insulin secretion, blood purifier, fever, sun stroke; Oldenlandia corymbosa to clear heat and toxins, activate blood circulation, promote dieresis and relieve stranguria (urinary obstruction), tumours of the digestive tract lymphosarcoma and carcinoma of the liver & larynx, appendicitis, hepatitis, pneumonia, cholecystesis, cellulites, snake bite, skin sores, ulcers, sore throat, bronchitis, gynaecologic infections & pelvic inflammatory diseases (Table 3). Therefore, losses of a single species may sometimes be more detrimental in terms of ethno-medicinal values. On the other hand, more than one weed species with different formulation were sometimes used for the treatment of a single disease. For example, dysentery is treated with 23 species followed by fever with 21 species, skin diseases with 20 species, asthma with 17 species, ulcer with 16 species, jaundice with 12 species, stomach-ache with 10 species, rheumatism with 9 species, urinary problems with 8 species, and malaria with 6 species. Diarrhoea and Diabetes, two of the most deadly diseases of the present era (www.healthline.com/health/top-10deadliest-diseases#copd), are also treated with eleven and seven weed species, respectively (Table 3).