- ‘Weeds’ are plants with special botanical and ecological attributes that allow their rapid establishment in disturbed areas, helping to reduce erosion of soils.
- Many weedy species have also proven their usefulness as medicines and food, going back several millennia. Wildlife, too, can benefit from such plants.
- Yet these plants are often the focus of a ‘war on weeds’ which is unfortunate and misguided, the author of a new book on the topic argues. “Can weeds be appreciated for their critical ecological roles? Can they be managed in situations where they may become problematic?” he asks.
- This post is a commentary. The views expressed are those of the author, not necessarily of Mongabay.
As a group of plants, weeds are unloved by some people. However, this dislike is not universal. Weeds are colonizing, pioneering plants, with special botanical and ecological attributes that allow them to succeed in ‘disturbed’ habitats.
Weedy species are a critical component of Mother Earth’s rich biodiversity. As frugal, thrifty and simple beings, which never ask for too much but give back more than they take, weeds are nature’s gifts from which humans can learn many lessons.
Weeds also spotlight the mistakes humans have made in managing our environmental assets by large-scale land-clearing, destruction of vegetation and soil resources, as well as unsustainable agricultural practices and urban development.
In a new book on weeds, I attempt to create a ‘storehouse of weedy information’ to enlighten general readers on the history of weeds and how to relate to them more effectively, with ecological understanding and empathy.
Weeds have special botanical and ecological attributes related to life cycles, growth habits, reproduction and dispersal that allow establishment in disturbed areas and their easy spread into new habitats.
In exploring the history of weeds and the origins of the definitions and terminology associated with weeds, it becomes clear that all weeds are nothing but colonizing plants, which grow and thrive in disturbed habitats and environments, especially those modified by humans.
But weedy species are not limited to human-modified environments. Natural disturbances, such as those caused by floods, cyclones, wind, fire and the like, also create conditions in which habitats are ‘opened-up’ for the colonizers to move into. Needless to say, weeds are highly opportunistic plants. They are very good at grabbing the opportunities created by disturbances and are indeed stimulated to grow by disturbances (such as when you dig into your garden bed).
From agricultural beginnings now dating back to well over 12,000 years of human history, weeds have been our constant companions. They have followed us wherever we went, and as phenomenally successful plants, weeds earned humankind’s wrath, almost as if humans are not able to psychologically cope with other successful and ‘pest-like’ species (for instance, the house fly, European rabbit, European fox, Indian mynah, and a host of others).
Stories about weeds that are mostly written and read in popular media, including the internet, are mostly concocted to invoke fear and loathing instead of a proper ecological understanding. Whether or not inadvertently created, these negative narratives often reflect a form of nascent xenophobia and anxieties in the general public about ‘immigrants’ who arrive at new locations, having left their ‘native’ places of origin.
Many weedy species have long been invaluable herbal medicines and food, going back several millennia. Such uses are apparent in the ancient scrolls found in the Egyptian pyramids, the Ebers Papyrus, as well as a vast volume of other literature dating back to the writings of ancient Greeks (Aristotle, Theophrastus and Dioscorides) and Romans (Pliny The Elder). Understanding these historical uses of weed species by humans as sources of dyes, essential oils, gums and resins is essential to appreciating the value of many species for livelihoods.
Colonizing species are also the ‘ecological Red Cross’ that rushes to help stabilize and restore lands cleared of vegetation by the human hand or natural disasters. They can also be effectively used in the ecological restoration of damaged ecosystems, such as parks, mines, and sites polluted by industrial effluents and discharges. A much-understated utilization opportunity is the capacity of fast-growing, colonizing taxa to take up, remove and sequester pollutants from contaminated land sites or waterways. No slow-growing ‘native’ species can remove pollutants and remediate contaminated sites.
Powerful and emotive phrases like ‘war with weeds’ are commonplace in such discourses, especially in developed countries, such as the U.S., Canada, Western Europe, Australia and New Zealand. This war has led to various groups such as ‘weed busters’ and ‘weed warriors,’ whose efforts at controlling weeds are by and large of limited local success, and essentially unsustainable in the long term.
More importantly, such antipathy towards weeds are not universal. Many African, South American and Asia Pacific developing nations and emerging economies are now questioning why weeds are blamed for always being an agricultural production constraint, or why we cannot manage our ecosystems better. Agroecology concepts show that for many thousands of years, humans and other animals have tolerated and co-existed with weedy species. Other animals and plants happily co-exist with colonizing species. Their mutual dependence extends to the provision of resources, such as pollen and nectar for animals and gene exchanges between related species, which drive plant evolution forward.
In discussing the evolution of weeds and their closely-related crops, I argue that weedy species have been crucial to human survival by being the progenitors of all of our food crops.
Traditional cultures in such societies greatly value species such as Centella asiatica (gotu kola), Alternanthera sessilis (lesser joyweed), Ipomoea aquatica (swamp morning glory), Portulaca oleracea (purslane), Basella alba (Ceylon spinach), Taraxacum officinale (dandelion) and a large number of other ‘edible weeds.’
A vast range of ‘healing weeds’ have been known from the times of ancient Egyptians, and include Papaver species (poppies, opium), Cannabis sativa (marijuana), Catharanthus roseus (Madagascar periwinkle), Datura stramonium (jimsonweed or devil’s trumpet), Bacopa monnieri (water hyssop or ‘Brahmi’), Asparagus racemosus (shatawari or hathawariya), Cardiospermum halicacabum (balloon vine), and the now world famous gotu kola. Many species are the only sources of critical, life-saving western medicines used in cancer treatments (such as the vincistrine alkaloids from Catharanthus roseus), pain relief (morphine, codeine, and many other opiates, obtained from Papaver somniferum and its relatives) or various other herbal drugs used in the treatment of central nervous system, bladder and kidney disorders.
Colonizing species, such as common reed (Phragmites australis), cattails (Typha species) and even water hyacinth (Eichhornia crassipes) play critical roles in purifying and remediating waterways by absorbing and retaining urban pollutants. Many are important in stabilizing food webs in disturbed environments.
A vast array of fast-growing species, such as wattles (Acacia species) and mesquite (Prosopsis spp.) are critical biofuels for rural people as firewood and biomass for biogas and power generation. Weedy colonizers that are large, fast-growing grasses such as giant reed (Arundo donax), switchgrass (Panicum virgatum), giant miscanthus (Miscanthus x giganteus), king grass (Pennisetum purpureum) and jatropha (Jatropha curcas) are undisputed ‘kings of grasses’ and sources of bioenergy.
Many colonizing taxa are heavy metal accumulators or hyper-accumulators that can be used to remediate polluted lands and waterways and mitigate pollution caused by cadmium (Cd), nickel (Ni) and even radioactivity. As I discuss in the book, the greatest opportunities for sustainable futures are in eco-friendly technologies that can use large, biomass-producing colonizing species for multiple purposes, such as pollution removal and bio-energy generation. Water hyacinth, common reed, cattails and many other weeds, often derided for being ‘invasive’ are among the best examples of such under-exploited potential.
The utilization of many species as sources of essential oils, plant dyes and plant fibers goes back more than 5,000 years of human history. These categories of uses are globally under-explored.
See related commentary: Is invasive species management doing more harm than good?
Looking at weedy species through the lens of utilization will prove that some of these species are, arguably, the ‘best-of-the-best’ with ecological attributes that can heal the planet and help humans and other animals survive uncertain times.
In joining the chorus of ‘un-winnable wars with weeds,’ the public is largely misinformed about weeds, with only one side of the story. Some weed scientists and ecologists are also, unfortunately, in this camp. Most weed research articles start with the viewpoint that ‘weeds cause biodiversity losses,’ as if that is an axiom.
Blaming weeds for the human follies of mismanaging our fragile earth is common. Weeds are also called ‘the second greatest threat to biodiversity’ on the earth, a highly contentious viewpoint.
I anticipate a critical dialogue on weeds, across borders that separate divergent views. Can weeds be appreciated for their critical ecological roles? Can they be managed in situations where they may become problematic?
A change in basic assumptions to tolerate the extraordinarily resourceful weedy taxa (‘living with weeds’) appears prudent, as plants and animals – as well as human societies – face uncertain times in a changing global climate.
Human psychology is involved in our responses to weeds. In promoting the virtuous side of weedy taxa, I argue for a better understanding of weeds as part of nature, and ending unsustainable approaches, such as a ‘war-with-weeds.’
Nimal Chandrasena is Editor-in-Chief of Weeds (the official journal of the Asian-Pacific Weed Science Society) and author of The Virtuous Weed. He obtained his Ph.D. in Weed Science from the University of North Wales.
Related audio from Mongabay’s podcast: For a discussion of the amazing world of plants and the challenges inherent in the current decline of the field of botany, listen here:
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