Botany

Some people, particularly in developed countries, have strong negative attitudes towards weeds, and a tendency to label potentially useful plant resources as invasive ‘aliens’, which are to be controlled at any cost. This undesirable attitude ignores the considerable evidence of beneficial uses of weed species to many societies, over a long period of human history. The recent application of ‘species-focused’ weed risk assessments have contributed to the maligning of many plant taxa as  ‘invaders’ in the public’s mind, undermining their worth as biological resources. Some of the methods used in the blitz against weeds, including the excessive use of herbicides, have resulted in undesirable consequences, such as herbicide resistance, and negative impacts on biodiversity in farming landscapes. Weeds maintain the biological diversity of farming landscapes, providing food and shelter for a variety of animals. Insects, which pollinate crops, extensively use weeds as a source of nectar, when crops are not in flower. Weeds also attract crop pests; and there is evidence that pest populations in some crops are much lower in ‘weedy fields’ than in ‘weed-free’ crops. As many of our primary crops have ‘weedy-relatives’, the genes present in weeds appear crucial for future evolution of crops, particularly to confer ‘hardiness’ (ability to tolerate variable environmental conditions). Some weed species contribute to aesthetic pleasure, as part of ‘wild nature’, while others provide culinary delights for humans, and are important as food sources for both vertebrate and invertebrate animals. Many weeds with medicinal values continue to be used either as traditional ‘herbal’ remedies, or extracted for secondary metabolites. The colonising strengths of several species are being used in the remediation of water and terrestrial environments to scavenge soil pollutants. Globally, there is considerable interest in using the large biomass produced by these species as raw materials for countless household products, including bricks, paper and furniture; and as future bio- fuels.Therefore, within the field of weed science, a fresh look at weeds is essential. Perhaps, a new and bold paradigm should be ‘co-existing’ or ‘living with weeds’, recognising their intrinsic worth as part of biodiversity,
and the many possible uses as bio-resources.
Key words:  Beneficial effects of weeds, Colonising species, Utilization of weeds, Weeds as biological resources

In tropical Sri Lanka, Water Hyacinth [Eichhornia crassipes (Mart.) Solms.] and Salvinia (Salvinia molesta DS Mitchell) continue to dominate eutrophic waterways in both rural and urban environments. In addition, several other highly invasive species have also ...

Submerged aquatic plants pose problems in Australian and New Zealand waterways for navigation, flood management, bank erosion, recreation and aesthetics. Among problematic species are: Lagarosiphon (Lagarosiphon major (Ridley) Moss), Egeria (Egeria densa Planch.), Hornwort (Ceratophyllum demersum L.) and Elodea (Elodea canadensis Michx.). These species prefer clear water, where they form dense stands. The problem in controlling these plants relates to

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