1. Introduction

Weed is the generic word for a plant growing in a spot where it is not wanted. The most prominent use of the word is in connection with farming where weeds may damage crops when growing in fields and poison domesticated animals when growing on pasture land. Many weeds are short-lived annual plants, that normally take advantage of temporarily bare soil to produce another generation of seeds before the soil is covered over again by slower growth; with the advent of agriculture, with extensive areas of ploughed soil exposed every year, the opportunities for such plants have been greatly expanded ^[3].

Etymologically, "weed" derives from the Old English word for "grass" or "herb," but during the Middle Ages the meaning has changed to indicate an undesirable plant that grows where it is not wanted, especially among agricultural plots. This has historically been the primary meaning of the word, although in the nineteenth century, American writers grew increasingly aware that calling a plant a "weed" was an arbitrary human judgment, as there is no natural category of weeds. In the words of Ralph Waldo Emerson, a weed "is a plant whose virtues have not yet been discovered." Today, biologists tend to share that opinion, since many of the plants that are designated as weeds are, in fact, closely related to popular crops. Indeed, "weed" has fallen out of usage among biologists, although those who study agriculture still find the term useful in discussions of weed control and management ^[24].

Generally a plant growing where it is not wanted is considered as weed. The notion of weeds as unnecessary plants was originated when man started to intentionally grow plants for food. Weeds are unnecessary plants because they are dropping crop yield by competing with crop plants for common resources such as water, mineral nutrients, space and light ^[13].

The plants of Rajshahi exhibit diverse habitats, such as wetland, scrub jungles, fallow lands etc. which support luxuriant formation of angiosperms and play a vital role in the local economy, environment and primary healthcare system. The importance of studying local floristic diversity has been realized and carried out in Bangladesh by ^{[8, 9, 16, 22, 23]}. Recently ^{[17, 18, 20, 21]} conducted the inventorying of angiosperm diversity of Dhamrai Upazilla of Dhaka and Runctia Sal forest of Bangladesh. The present study will be made an inventory of the angiosperm weeds of Rajshahi, Bangladesh.

2. Materials and Methods

Assessment of angiosperm weeds growing throughout in the Rajshahi, Bangladesh was carried out from January 2010 to December 2011. A total of 155 species under 125 genera and 50 families were collected and identified. A survey on the determination of the location of different species was made and a list was prepared to be acquainted with the plants available in the selected area. All the species were noted and time to time the areas were visited to see when they flowered. For the morphological study, different types of species were examined again and again in order to see if there was any variation or not. They were collected at flowering stages and herbarium specimens were prepared as vouchers. In this practice standard method was followed. In this regard different types of plant species were collected from different habitats. All the collected plant specimens were kept in the Herbarium, Department of Botany, and University of Rajshahi, Bangladesh.

The collected specimens were identified studying related taxonomic books and booklets from the library of Rajshahi University. The major collected materials were identified and described up to species with the help of ^{[1, 2, 4, 5, 7, 10, 12, 13, 14, 15, 19]} were consulted. For the current name and up to date nomenclature ^{[1, 6, 11]} were also consulted.

3. Results and Discussion

In the present paper occurrence of 155 angiosperm weed species under 125 genera and 50 families were recorded. Of these, Magnoliid Complex (Eudicots) ^[7] was represented by 138 species under 109 genera and 43 families while (Monocots) ^[7] was represented by 17 species under 16 genera and 7 families. Asteraceae were the largest family in Euasterids II ^[7] represented by 27 species and Araceae were the largest family in Alismatales ^[7] represented by 6 species. An enumeration of the species recorded was presented with scientific name, bengali name, family, population, flowering time and voucher numbers. Out of the total number of species 98 were frequent, 41 were abundant, 15 were rare and 1 was very rare species in the study area (Table 1).

Distribution of angiosperm species in the families shows variation. The family Asteraceae is represented by 27 species, Fabaceae is represented by 14 species, Acanthaceae by 11 species, Amaranthaceae by 9 species, and each of Lamiaceae, Solanaceae and Araceae is represented by 6 species. Euphorbiaceae is represented by 5 species; A single species in each was recorded by 24 families while two to four species in each was recorded by 18 families (Table 1).

Among the species studied Blumea laciniata (Roxb.) DC., Cyanthillium cinerum (L.) H. Rob., Sphagneticola trilobata (L.) Pruski. and Wedelia biflora L. have been reported here for the first time from Rajshahi, and Parthenium hysterophorus Linn. was a new record from Bangladesh.

Table 1. Assessment of angiosperm weeds of Rajshahi, Bangladesh

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The important medicinal weedy plants of Rajshahi were carried out. A total of 50 medicinal plant species belonging to 46 genera and 31 families were collected and recorded for their use in various ailments. Most of the local people in the study area are poor are illiterate. In one hand, these people are out of the reach of modern medicines and on other hand, the market price of most available medicines are very expensive. As a result, these medicinal plants are used by them to cure following the diseases, especially for abscess, asthma, abortion, cough, cold, small pox, constipation, dysentery, diarrhea, diabetes, eczema, fever, and fracture of bone, headache, heart disease, itches, jaundice, menstrual disease, paralysis, piles, skin diseases, snake-bite, toothache, vomiting, worm, wound and others. Different plant parts of different spp. are used as medicine for treating various diseases; bark of 3, leaf of 34, fruit of 3, root of 19, seed of 1, latex of 2, stem of 5, mucilage of 1, inflorescence 1, rhizome 1, tuber 2 and whole plant of 13 species were used as medicine (Table 2).

Table 2. Medicinal angiosperm weeds used by local people of Rajshahi, Bangladesh

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4. Conclusions

Assessment of angiosperm weeds of Rajshahi, Bangladesh has been studied. A total of 155 angiosperm weed species under 125 genera and 50 families were recorded. Fifty (50) medicinal plants have been documented with their uses for the cure of more than 61 diseases, and some of these are abscess, asthma, abortion, cough, cold, small pox, constipation, dysentery, diarrhea, diabetes, eczema, fever, and fracture of bone, headache, heart disease, itches, jaundice, menstrual disease, paralysis, piles, skin diseases, snake-bite, toothache, vomiting, worm, wound and others. This detailed information will be helpful for the pharmacognosist, botanist, ethno-botanist and pharmacologist for the collection and identification of the plant for their research work.

Acknowledgements

The author is grateful to the Ministry of Science, Information and Communication Technology, Government People’s Republic of Bangladesh for financial support to complete this research work.

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