HORT travels

Exploring the horticultural beauty in every adventure.

Defense

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“No matter how intently one studies the hundred little dramas of the woods and meadows, one can never learn all the salient facts about any one of them.”

― Aldo Leopold, A Sand County Almanac and Sketches Here and There

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Prickles and tendrils of our native Greenbriar (Smilax rotundifolia) along the Appalachian Trail on the way to the Pinnacle.

With the many types of media that surround us, the goings-on around the world filter into the everyday, and sometimes the every moment. Heartache and heartwarming happens with stories of how humans decide to interact with the world and people around them. Rarely do stories making the news include tales of people-plant interactions, yet these stories happen every day as well. Each second plants are interacting with the world around them whether it is with animals, humans (we are animals, yes?) fungi, or other plants they are constantly on the defense. Sort of like people lately, it seems.

Unlike people, plants cannot just get up and remove themselves from a situation (makes me wonder since people CAN do that, why don’t we do that more often?). But just like people, plants have developed a variety of ways to protect themselves from harm. And other residents in nature have found ways to exploit these defenses for their own survival.

Soft and Gentle

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The soft, soft leaves of Common Mullein in a roadside fallow field in Southeastern PA.

 

Some plants choose the soft subtle way of deflecting harm. Perhaps you know a person like this as well. Plants that have soft hairs do not have these just for decorative reasons (rarely in nature is anything purely decorative).  Plants like the common mullein (Verbascum thapsus) and lamb’s ear (Stachys byzantina) sport hairs so soft you can’t help but pet them and perhaps rub them against your cheek (please tell me that’s not just me that does that!) or imagine a the softest blanket made of the leaves. These hairs are not for our entertainment, they protect the plants. The hairs make a meal of mullein or lamb’s ear an unenjoyable experience that happens only in the most dire of circumstances. These soft hairs quietly and subtly defend the plant from being eaten.  In addition, these hairs help keep the plant’s moisture in. These soft hairs cover the plant’s pores (stomates) which are used to exchange gasses and water as the plant grows. These hairs make it so, in times of drought, the plant is able to hold on to the water.

But these hairs are put to good use in addition to helping the plant from becoming dinner and losing all the water its roots took up. The hairs on these plants may become part of the cozy interior of a hummingbird nest. One feature of nature’s protection becomes another’s home.

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A hummingbird observing the garden at Desert Botanical Garden in Phoenix, AZ

Armored

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The distinctive bark of Flowering Dogwood at Laurelwood Arboretum in Wayne, NJ

Some plants have their guard up all the time. There is no doubt they are trying to protect themselves at all moments from all danger, real or perceived. (Know any people like that?) Bark is a terrific example of constant protection. Bark is the protective layer of a tree or a shrub. Its purpose is to protect the very thin, very fragile vascular system of the plant from harm (think of our skin protecting our veins just below the surface – bark is doing the same thing). This harm may come in the form of friction from other trees and shrubs rubbing against it, the gnawing teeth of rodents or the wicked whirr of a weedwacker.

Bark is great for us, and the other animals that use this tree or shrub, to use for identification because it is always there. After the leaves have fallen and the flowers have faded that trusty bark remains. In fact, this protective layer not only protects the fragile inner-workings of the tree, it may end up protecting something else.

Beneath the flakes and peels of Shagbark Hickory bark you may find overwintering moths,  or during the warmer months you may find bats hanging out.

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The flakes and flaps of Shagbark Hickory bark at Bowman’s Hill Wildflower Preserve in New Hope PA

Sharp and Pointy

A Mammularia...I think.  Cactus flower!

A large pink flower on a small spine covered cactus at the Desert Botanical Garden in Phoenix, AZ

Nothing says “stay away from me” better than spines, prickles and thorns emanating from all angles. Various trees, shrubs, vines and herbaceous (no bark) plants sport various pointy protections. Of course what probably immediately comes to mind when spiny plants are mentioned is the cactus.

What look like thorns on plants are actually very different, though, their purpose is the same. Typically plants may have spines, thorns or prickles.

Spines – like those found on cactus are actually modified leaves. Plants lose 99% of their water through their leaves (this creates the vacuum system that enables water to be taken up through the roots – plants are amazing!). This losing of water may be fine where water is plentiful and regularly available, but if the plant lives in a desert, this losing of water through leaves – not such a great thing. So these leaves have become smaller, thinner over time reducing their surface area so water does not leave (protection #1). These thinner, harder leaves now also protect the fleshy parts of the plant from desert dwellers looking for moisture rich food (protection #2).

These spines may also become protection for others. Animals find safety in the spine covered plants, finding security from those who may do them harm in the sharp spines of cactus plants.

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Heart-shaped hole created by a bird in this saguaro cactus in Desert Botanic Garden, Phoenix AZ.

Thorns –  Thorns are modified shoots of a plant. They arise from a bud, or growing point on the plant. They still offer protection to the plant, and to animals calling the plant home or dinner, but they function on the plant differently. Thorns may be branched and may have leaves.  Some plants featuring thorns are the honeylocust and hardy orange.

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The thorns and fruit of Hardy Orange (Photo from Wikimedia commons)

Prickles – What we usually call thorns, those sharp things on roses, are actually prickles! These are modified skin of the plant (the epidermis) and can arise from anywhere on the plant. They come off the plant easily because they are not attached to the vascular system of the plant like spines and thorns, which is why you end up with rose ‘thorns’ in your thumbs when you are doing some pruning. You may notice that on many plants the parts that support the fruit are prickle-, thorn- or spine-less. The plants want to ensure the next generation moves about in the world. Fruits surrounded by thorns are not moved around easily, but shiny fruits easily accessed make it through the woods and meadows in no time.

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The prickles of an ornamental rose at the Scott Arboretum of Swarthmore College in Swarthmore, PA

Some plants feature one or more of these sharp and pointy protections:

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Wineberry features thorns and prickles.

Toxic Protections

Some plants choose to poison their attackers. Certain plants let you know they are dangerous and to approach at your own risk while others keep their secrets to themselves until you decide to attack them, assuming you will learn your lesson and not attack again.

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The chemical-filled trichomes of Stinging Nettle along the Perkiomen Trail in Green Lane, PA

Stinging Nettle (Urtica dioica) is one of those plants that announces the discomfort you may feel when engaging this plant. Tiny trichomes, or miniature hypodermic needles, cover the leaves and stems of this plant. When brushed against they inject various chemicals into the attacker resulting in the pain of a million bee stings (or something like that). My first encounter with this plant was going off trail through a meadow in sandals. I didn’t know this plant then. I learned it really quickly. Stinging nettle between the toes is not anything I want to experience again, so I learned this plant very well. However, this plant is known for its medicinal properties. It is juiced and eaten by many people and its stinging trichomes have been used for arthritis treatment.  And as much as I have zero interest in eating this plant, it is an important larval food source for a variety of butterflies, and certain butterflies need it exclusively.

Other plants  choose to keep their toxic protection hidden. The most famous of these may be poison ivy.

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The flower buds and shiny new leaves of poison ivy.

Poison Ivy (Toxicodendron radicans) not to be confused with our fantastic sumacs contains a chemical compound  (Urushiol) to which many of us have a reaction. Poison ivy berries are an important food source for migrating and overwinter birds and the leaves are eaten by many mammals. Many other mammals, birds and even amphibians find shelter among the seemingly harmless leaves and stems.

Understanding the Defense

At the top of this post there is a picture of the native greenbriar. I grew up with this plant tugging at my pant legs and arm sleeves as I explored the woods of my pine barrens home. The constant bright green of the stems and leaves always intrigued me so I carefully removed myself from its grasp and carried on with my explorations. Little did I know then what these ‘thorns’ were protecting. What many people consider a weed, uses its green prickles to protect its fruit to feed many species of birds. It is not entirely covered in sharp appendages, and young shoots are prickle-free, allowing for numerous mammals to eat the green foliage when not much is left in winter months, the stems and leaves create fortified shelters for small mammals and many birds.

You see, plant defenses are varied. Often they are there to protect themselves while also protecting the insects, birds, amphibians or mammals that aid them in the spread of their seeds, their continuation of the species. Some tell you right away “leave me alone” while others let you get close then fight back. Some exhibit softer gentler ways of protecting themselves without causing harm to others while some have sharp and pointy ways of defending themselves. Perhaps we can learn a lot from the defense mechanisms of plants about the defense mechanisms of people. We never know what the plant may be protecting besides its own life and we cannot always predict what will happen by looking at the exterior.

 

2 thoughts on “Defense

  1. Pingback: Vulnerability | HORT travels

  2. The wonders of nature are without a doubt simply fascinating! Mother Nature seemed to take every thing into account. Every thin serves a purpose and the closer we observe, the more we see, She did nothing by accident. Many a time I have been left bleeding after pruning and cleaning up shrubs and plants with thorns After i get done cursing and bandaging myself, I realize that really l it’s a small price to pay. Without these features which often times serve as protection,.. we might be robbed of of ever seeing the beauty in them. So I am careful mow when pruning Roses. I wear gloves, and when trimming Pyracantha or cleaning out the debris beneath them, I prefer to use a hand blower and then wear gloves (leather ones to pick up the waste I have blown out.

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