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The Amazing Resilience of Weeds: A Review of Richard Mabey’s "Weeds: In Defense of Nature’s Most Unloved Plants"

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The Amazing Resilience of Weeds: A Review of Richard Mabey’s "Weeds: In Defense of Nature’s Most Unloved Plants"

In his book Weeds: In Defense of Nature’s Most Unloved Plants, English nature writer Richard Mabey states that plants that “obstruct our plans, or our tidy maps of the world” are weeds. The difference between weeds and what might be termed respectable plants is not so much botanical in nature but the result of human judgments on their respective value. Weeds grow where they are unwanted and crowd out the plants we deem valuable, such as crops and ornamental flowers, or they mar meticulously planned gardens. Mr. Mabey thus calls weeds “trespassers,” “vegetable guerillas,” “outlaws,” and botanical “fifth columnists.”

Weeds suffer in our estimation not only from their annoying invasiveness but also from the dismal places in which they live, namely among urban blight, environmental devastation, and trash dumps. In doing so weeds acquire the disrepute that more properly belongs to the slovenly people who debase the properties where they reside, what Mabey terms “guilt by association.” For example, In hardboiled detective stories, where cases often lead to badly maintained houses in sketchy neighborhoods, weeds abound alongside torn window screens, peeling paint, yellowed newspapers, litter, and rings of motor oil on the cracked driveways. Weeds are synonymous with neglect.

Kudzu vine.

Kudzu vine.

However, they hardly are botanical bums. They are relentless opportunists that adapt and thrive where other plants cannot. They earn Mabey’s admiration for their persistence in adapting to whatever environment they find themselves in and the clever ways they go about doing so. “They are unfussy about where they live, adapt quickly to environmental stress, use multiple strategies for getting their own way. It’s curious that it took so long for us to realize that the species they most resemble is us.”

It has long been said that the only survivors of nuclear war will be cockroaches and Keith Richards. I put my money on weeds.

This is not to say that Mr. Mabey is entirely sold on the weed community by virtue of its ubiquity and determination to survive. For one thing, he notes the ugliness of many of its members.  More serious is the rampant growth of superweeds such as kudzu, that are glyphosate-resistant, i.e., Roundup-tolerant. Superweeds spread from continent to continent and are frightening in not only their destructiveness and refusal to be controlled, but in some cases, their grotesque size. Horseweed grows to six feet high, and the Palmer amaranth reaches eight feet while developing a stem so tough it can damage farm machinery. Sound like a monster movie? In a desperate effort to halt the invasion of superweeds, newer herbicides have been developed, some of which even use components of the notorious Agent Orange.

Bindweed.

Bindweed.

Our City Forest uses nontoxic measures to control weeds. Over the years Volunteers and AmeriCorps members have been a great help in hand weeding OCF’s Community Nursery and Martial Cottle acreage. In addition, weed cloths and mulch-covered cardboard are used at both sites. A recent blog related how OCF’s Lawn Busters effectively use cardboard and mulch in converting weed-ridden lawns to drought-resistant, weed-free xeriscapes.

So how did weeds acquire their tenacity?  Why do they survive in places that are alien to the rest of the botanical world?  One reason, according to Mabey, is they originated in places of continual disturbance where adapting to such conditions was necessary for survival. Weeds, he writes, “evolved on tide-pounded beaches and the precarious slopes of volcanoes, in the flood zones at the edges of rivers and the muddy wallows made by wild grazing animals, in scree and shingle and glacial moraines.” No wonder weeds are tough cookies. Plants that live in such turbulent and unstable conditions must develop special characteristics to survive.

As a consequence of their background, many weeds germinate quickly and have expedited life cycles. They jump at brief windows of life while spreading prodigious numbers of seeds. Some seeds have barbs that catch on to passing animals and  spread wherever the animal travels. Other seeds lie dormant for remarkably long periods of time and eventually germinate when conditions are right.  For example,  species not seen for decades sprouted in the rubble created by German bombing of London in World War II.  Even more remarkable are recent archaeological digs in the UK at ancient Roman sites that prompt dormant seeds to sprout that are up to 2,000 years old!  If a seed company marketed packets of weed seeds (an unthinkable idea), how would the “use by dates” read?   Best if used by December, 2077?  July, 4017?

Foxtail.   

Foxtail.

 

Lastly, through natural selection over countless growing seasons, some weeds mimic the appearance of neighboring crops to ensure that their seeds are harvested along with the host crops. In Southeast Asia, weed grasses have become indistinguishable from rice. In the case of wheat, Mabey writes that “cutting it every autumn with a sickle perpetuated weeds whose seeds were produced at the same height as the wheat ear.  Sieving grains favored weed seeds most similar in size to the crop’s.”

This charming and informative--and occasionally frightening--book goes beyond weeds’ ability to propagate and endure. For instance, Mr. Mabey, in what he calls the “human story of weeds,” considers man’s long and  troubled relationship with weeds. Some species possess, or were once  believed to possess, special medicinal properties. Hence they go in and out of fashion. Use of herbicides actually end up benefiting weeds by increasing their tolerance to them. Spraying tons of Agent Orange on rainforests in Viet Nam killed the trees but allowed a tough grass called cogon to flourish in their place. Once checked by the forest’s shady canopy, cogon now thrives in Viet Nam’s defoliated landscapes..  

Field infested with Palmer amaranth.

Field infested with Palmer amaranth.

In spite of their astonishing resilience and contributions to the health of the planet, such as retaining topsoil (see Mark Schonberg’s article, “An Ecological Understanding of Weeds” for other benefits provided by weeds), weeds remain a tough sell. Think mosquitoes and viruses. The fact that something is adaptable and tenacious does not make it endearing.  Flowers and shrubs, on the other hand, may be wimpy in comparison to weeds, but they are far easier to love.

For Further Reading:

Mark Schonberg, “An Ecological Understanding of Weeds,” http://articles.extension.org/pages/18529/an-ecological-understanding-of-weeds

 

 

 

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Coral Root: Parasite in the Redwood Forest

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Coral Root: Parasite in the Redwood Forest

The orchid family, Orchidaceae is enormous, containing 28,000 species. That’s just slightly more species than the population of Monterey, California. The species count does not include the 100,000 or so cultivars that have been bred by humans. California has only 31 native orchids (most of them live in the tropics). I didn’t realize that I had seen my first one.

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Growing and Taming the Matijila Poppy

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Growing and Taming the Matijila Poppy

Five feet tall, and half a foot wide, a white flower with bright gold stamens in the center, loomed over the nursery path. Since moving from Michigan four months ago, I had yet to see a plant that really blew me away. 

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Everything You Ever Wanted To Know About Plants, Part 7: When is a Berry a Berry?

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Everything You Ever Wanted To Know About Plants, Part 7: When is a Berry a Berry?

With spring and summer come farmers markets and a wide variety of fruits and vegetables. In the next two months, berries of a ton of different varieties come into season including, strawberries, raspberries, blackberries and blueberries. Well, I say berries but really only one of the berries mentioned is actually a berry. Guess which one? I’ll wait. As the narrator of a blog piece about botanical fruit varieties I have infinite time.

Give up?

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Everything You Wanted to Know About Plants Part 2: The Conquest of Land

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Everything You Wanted to Know About Plants Part 2: The Conquest of Land

Last week, I introduced the concept that green algae (but not their brown, red and gold counterparts) are actually plants that outnumber the leafy things we're all familiar with. You were probably left wondering how one gets from Ulva and Volvox to a redwood. As it turns out differences between land plants and green algae have everything to do with the different environmental challenges they face.

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Everything You Ever Wanted To Know About Plants (And More): Part 1

All throughout fall we at Our City Forest receive panicked emails from residents about their trees. Everywhere it seems that young, healthy trees planted earlier this year are dying. People blame lots of things for this, the drought, insects, poor soil, or even Our City Forest. More often than not the blame rests on autumn. In New England the height of the leaf season has come and gone. The hills are no longer awash with red, yellow and orange, or smell of leafy petrichor, crisp on cold winds. Here in San Jose, deciduous trees (trees that shed leaves) are at the tail end of the fall color season, entering their winter dormancy.

It's hard to believe that this happens every year. 

It's hard to believe that this happens every year. 

We don’t blame people for not knowing about autumn. Many people in the region come from subtropical areas with long growing seasons. Many more have no direct experience with plants, trees and the peculiarities of seasonal changes. This is the first part of a multi-part series on plants, plant science and arboriculture to shed light on our photosynthetic friends (in a metaphorical sense).

Plants love light after all. 

Plants love light after all. 

When I say “plants” chances are you picture big, leafy trees, flowers, shrubs and maybe some of you think of ferns and moss. All of these images are correct but incomplete. Land plants, the plants most humans are familiar with, actually constitute a small fraction of the diversity of the Plant Kingdom.

The vast majority of plants, by population, are actually aquatic, green algae. (Flowering plants dominate other plant types in terms of species richness). Like the plants you're familiar with, they come in a variety of shapes and sizes. Most are microscopic but many are visible to the naked eye and come in a variety of shapes and sizes. From nesting, spherical Volvox to leafy, filmy Ulva green algae dominate the plant kingdom. (Not kelp though, that’s brown algae).

The variety of green algae in the sea is stunning 

The variety of green algae in the sea is stunning 

So what makes a plant a plant? All plants, as it turn out, have similar cellular structure. Plant cells are eukaryotic, meaning they have an array of membrane-bound organelles, including a nucleus. All have cell walls made of cellulose, which provide the cells with structure and protection.

A plant cell. Note the cell wall, vacuole and chloroplasts 

A plant cell. Note the cell wall, vacuole and chloroplasts 

Plants also have chloroplasts, specialized double-membrane organelles for photosynthesis containing “a” and “b” type chlorophyll pigments. Chloroplasts are thought to have arisen from symbiotic cyanobacteria that lived within the common ancestor of plants billions of years ago. Scientists have discovered they have their own, unique genome like mitochondria. Red and brown algae have chloroplasts also but their chloroplasts use different pigments and have more membrane layers. (They also go through distinctive developmental phases that plant cells do not go through). Plant cells also have large, central storage vacuoles that maintain the cell’s shape via turgor pressure.  

Wilting is in part caused by a lack of tugor pressure as the leaves lose water. 

Wilting is in part caused by a lack of tugor pressure as the leaves lose water. 

There are approximately 300,000-400,000 species of plants on Earth and more are described every year by botanists, ecologists and microbiologists. Almost 250,000 of these species are flowering plants (angiosperms). The next post in this series will focus on plant anatomy and physiology (did you know plants have hormones and that they do really rad things?) and after that we’ll focus on tree-specific topics. Hope you enjoy. 

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