Understanding the Prickly Parts of Plants

As a long-time avid gardener, I take pride in being able to identify most ornamental plants on sight. But weeds are another matter. Identifying the usual cast of weedy characters, like chickweed, henbit, and crabgrass, is no problem. As for more exotic or less common weed species, I confess my knowledge is somewhat limited. That was clear this summer when I didn’t know what a weed with little yellow flowers was that showed up in my perennial garden. It looked harmless enough, so I chose to ignore it.

As the days got cooler, this invader’s yellow flowers turned into groups of seeds that looked like spikes and had tiny barbs on one end. I discovered the seeds when I accidentally brushed against the plant. To my annoyance, dozens of those little barbs latched onto my shoes, socks, and jeans.

I became very interested in the barbs on those seeds as I thought about their shape and purpose. Lots of plant species worldwide are armed with sharp, pointed outgrowths. But why? What purpose do they serve? Clearly, this called for a little sleuthing to find some answers.

When I looked into it more, I found that these growths are different depending on where on the plant they are found. Specialists in plants and crime scenes will have to figure out how and when these structures formed. Why they evolved seems intuitive. Basically, some of them evolved as ways to protect plants from herbivores nibbling on them, while others evolved as ways to spread seeds.

Plant parts that are sharp and pointy are often called thorns, spines, or prickles. While the three terms are used interchangeably in casual conversation, botanically they are not the same. Each is an adaptation of a separate plant part.

Thorns grow in the leaf axil where a branch would normally grow, but they end in a sharp, hard, woody point. They grow from a plant’s stem tissue and contain internal vascular tissue (phloem and xylem). Native tree species like the Washington hawthorn (Crataegus phaenopyrum), the honey locust (Gleditsia triacanthos), and the black locust (Robinia pseudoacacia) have thorns that they picked up over time. Many non-native species have thorns as well, such as firethorn (Pyracantha) and Japanese flowering quince (Chaenomeles spp. ).

Here’s a little known fact: Most citrus trees such as lemons, limes, grapefruits, and oranges have thorns. Even stranger, apple, plum, and pear trees evolved with thorns as well, though modern varieties have been bred to not have any.

Spines are derived from a plant’s leaf tissue. They are hard, sharp, thin, pointed structures that look like a changed leaf or stipule (an appendage that grows at the base of a leaf stalk). Like thorns, spines also have internal vascular tissue.

In general, spines are found on most cactus species and on some succulents. When a leaf is turned into a narrow spine with less surface area, the plant can stop losing as much water. A flat, wide leaf can lose a lot of water. Spines help the plant get some shade, which is helpful in places that are hot and dry. Spines also seem to have developed to protect plants from birds and other animals that would eat them or try to get water from their cells.

Different types of plants, besides cacti, have evolved to have spiny parts on the edges or tips of their leaves. For example:

The edges of some trees and shrubs, like holly (Ilex) species, false holly (Osmanthus), and Oregon grape holly (Mahonia aquifolium), have spiny parts on the edges of their leaves. These marginal spines are extensions of the leaf’s major veins.

Having spines at the very end—Some plants, like Agave, Sansevieria, and Yucca species, have sharp points (called terminal spines) on the ends of their leaves.

Prickles are short, sharp, woody projections that come from the epidermis tissue of a plant. The epidermis is the single layer of cells that covers the leaves, flowers, stems, and roots of some plants. Think about it this way: a prickle is most likely to be a sharp, pointed growth on a plant that isn’t a branch or leaf. Unlike thorns and spines, prickles don’t have any blood vessels that connect them to the plant’s main body.

Some plants, like rose bushes, have prickles on the stems only. Oh, by the way, the “thorns” on rose bushes are not really thorns at all. Because they grow at random spots along the stems of the plant, that technically makes them prickles.

Greenbrier (Smilax) is an example of a plant armed with prickles on its stems. Even though it grows like a weed and has nasty prickles, this low-growing woody vine is native to North America and has some good points. The fruits are a food source for many bird species. After eating the fruits, they scatter them all over our land, which is why the plants seem to appear out of nowhere.

Other plants, like horsenettle (Solanum carolinense), have prickles on both stems and leaves. Horsenettle is a bothersome weed that occurs both in pasture fields and in home landscapes. There are prickles on the stems, petioles, leaf veins, and even the flower stalks of this plant. Because the plant is so prickly, animals are deterred from grazing. It turns out that this is a good thing because the plants and their fruits can hurt animals.

For yet other plant species, the prickles are attached at the base of the leaves only. Spiny amaranth (Amaranthus spinosus) is one such example. The very sharp, stiff prickles on this plant can be as long as a quarter of an inch. Also, a fully grown spiny amaranth plant can make around 235,000 seeds, which makes it a tough weed to get rid of.

A few plants have reflexed or recurved prickles, meaning that the tips point downward. This design hinders small animals from climbing stems to reach leaves on some plants. On some plants, especially ones with long stems, the prickles make it possible for the plant to attach itself to other plants or branches for support. A plant with reflexed prickles is Mile-a-minute vine (Persicaria perfoliata), which is very invasive and hard to get rid of.

There are a lot of plants with prickly personalities that don’t fit neatly into the three groups we just talked about. A few variations on a theme include the following.

Sticky parts on flower heads, seeds, or fruits—These kinds of structures make a lot of sense from an evolutionary point of view. For their species to stay alive, plants need to spread their seeds to new places where they will have less competition for food, water, and light. One very effective way for seeds to get to other places is to use special mechanisms that look like barbs and are made to help the seeds stick to things or hitchhike. According to Botany for Gardeners by Brian Capon, “hooks and barbs are a reliable sign that a seed or fruit is ready to hitch a ride on a passing animal.” ”.

Many plants have fine hairs or bristles that protect them from heat or cold and from herbivores, among other things. Prickly lettuce (Latuca serriola) is such a plant. The edges of these weed’s leaves are sharp, and there is a row of stiff, sharp bristles on the lower midvein. Between the prickly leaves and milky sap, this is not a pleasant plant. It is also quite prolific. According to Weeds of North America, a large, mature plant can produce up to 87,000 seeds!.

Burs: A bur, which is sometimes spelled burr, is a seed or dry fruit with hooks or teeth that are meant to keep herbivores away and spread seeds by sticking to fur or clothing. Depending on the plant species, burs can be a mild annoyance or a serious hazard. On the annoying side, they can snag or tear one’s clothing. Some burs are very dangerous because they can puncture tires, catch on animals’ legs or feet and hurt them, and damage farming tools used for harvesting.

Yes, even vegetables have their share of prickly personalities. For example, some types of eggplant have small spikes on their stems and on the calyx, which is where the fruit meets the stem. Grasping the stem at that point with bare hands can be painful. When you touch yellow squash plants with your bare hands, the stems and leaves can be painfully sharp. Even the fruits are covered with fine, nearly transparent hair-like bristles. Some, but not all, cucumber varieties have slightly spiny fruits as well as prickly stems. Artichokes have prickly leaves and beautiful violet-purple thistle-like flowers that attract pollinating insects. The flower bud that can be eaten has scale-like leaves with short, poisonous thorns on the ends that must be cut off.

Except for the vegetables, many of the prickly plants described herein are opportunists. They appear most often in disturbed soil, such as alongside roadways, construction sites, or garden beds. Beyond being blown around by the wind or carried by water, wild animals, birds, people, and our pets can also spread seeds. It’s important to get rid of the plants when they are seedlings for several reasons, no matter how they are spread:

If you change a thorn into a spine, you change a leaf or part of a leaf into a thorn. A prickle is an outgrowth from the epidermal tissue of stems, leaves, and some fruits. You don’t need to know the differences between these three unless you want to use that information to help you identify plant species. Keep in mind that not all plants with sharp or prickly outgrowths are weeds or even undesirable. Many of these plant species are valuable sources of pollen, nectar or shelter for pollinators and other wildlife. But it is important to figure out which plants aren’t wanted and should be gotten rid of before they become a problem. The best things you can do are stop them from planting seeds in the first place or get rid of them when they are seedlings.

As I think about the Beggar’s weed that led me to this discovery, I now understand and even admire how it stays alive. The plant is rooted in the soil and cannot move. That’s why, many thousands of years ago, its ancestors learned how to use moving things to spread their seeds. There’s even a term for this strategy: zoochory. Pretty clever, don’t you think?.

Featured photo: Common thistle armed with formidable prickles on stems, leaves and flowers. Photo: Pat Chadwick

David Trinklein wrote an article for the University of Missouri’s Integrated Pest Management that came out on January 3, 2013, called “Of Thorns, Spines, and Prickles.”

Piedmont Master Gardeners • Sharing knowledge, Empowering communities PMG News

• By Pat Chadwick
• /
• November 2021-Vol.7, No.11
• /

As a long-time avid gardener, I take pride in being able to identify most ornamental plants on sight. But weeds are another matter. Identifying the usual cast of weedy characters, like chickweed, henbit, and crabgrass, is no problem. As for more exotic or less common weed species, I confess my knowledge is somewhat limited. That was clear this summer when I didn’t know what a weed with little yellow flowers was that showed up in my perennial garden. It looked harmless enough, so I chose to ignore it.

As the days got cooler, this invader’s yellow flowers turned into groups of seeds that looked like spikes and had tiny barbs on one end. I discovered the seeds when I accidentally brushed against the plant. To my annoyance, dozens of those little barbs latched onto my shoes, socks, and jeans.

I became very interested in the barbs on those seeds as I thought about their shape and purpose. Lots of plant species worldwide are armed with sharp, pointed outgrowths. But why? What purpose do they serve? Clearly, this called for a little sleuthing to find some answers.

When I looked into it more, I found that these growths are different depending on where on the plant they are found. Specialists in plants and crime scenes will have to figure out how and when these structures formed. Why they evolved seems intuitive. Basically, some of them evolved as ways to protect plants from herbivores nibbling on them, while others evolved as ways to spread seeds.

PRICKLY PLANT STRUCTURES DEFINED

Plant parts that are sharp and pointy are often called thorns, spines, or prickles. While the three terms are used interchangeably in casual conversation, botanically they are not the same. Each is an adaptation of a separate plant part.

THORNS

Thorns grow in the leaf axil where a branch would normally grow, but they end in a sharp, hard, woody point. They grow from a plant’s stem tissue and contain internal vascular tissue (phloem and xylem). Native tree species like the Washington hawthorn (Crataegus phaenopyrum), the honey locust (Gleditsia triacanthos), and the black locust (Robinia pseudoacacia) have thorns that they picked up over time. Many non-native species have thorns as well, such as firethorn (Pyracantha) and Japanese flowering quince (Chaenomeles spp. ).

Here’s a little known fact: Most citrus trees such as lemons, limes, grapefruits, and oranges have thorns. Even stranger, apple, plum, and pear trees evolved with thorns as well, though modern varieties have been bred to not have any.

SPINES

Spines are derived from a plant’s leaf tissue. They are hard, sharp, thin, pointed structures that look like a changed leaf or stipule (an appendage that grows at the base of a leaf stalk). Like thorns, spines also have internal vascular tissue.

In general, spines are found on most cactus species and on some succulents. When a leaf is turned into a narrow spine with less surface area, the plant can stop losing as much water. A flat, wide leaf can lose a lot of water. Spines help the plant get some shade, which is helpful in places that are hot and dry. Spines also seem to have developed to protect plants from birds and other animals that would eat them or try to get water from their cells.

Different types of plants, besides cacti, have evolved to have spiny parts on the edges or tips of their leaves. For example:

The edges of some trees and shrubs, like holly (Ilex) species, false holly (Osmanthus), and Oregon grape holly (Mahonia aquifolium), have spiny parts on the edges of their leaves. These marginal spines are extensions of the leaf’s major veins.

Having spines at the very end—Some plants, like Agave, Sansevieria, and Yucca species, have sharp points (called terminal spines) on the ends of their leaves.

PRICKLES

Prickles are short, sharp, woody projections that come from the epidermis tissue of a plant. The epidermis is the single layer of cells that covers the leaves, flowers, stems, and roots of some plants. Think about it this way: a prickle is most likely to be a sharp, pointed growth on a plant that isn’t a branch or leaf. Unlike thorns and spines, prickles don’t have any blood vessels that connect them to the plant’s main body.

Some plants, like rose bushes, have prickles on the stems only. Oh, by the way, the “thorns” on rose bushes are not really thorns at all. Because they grow at random spots along the stems of the plant, that technically makes them prickles.

Greenbrier (Smilax) is an example of a plant armed with prickles on its stems. Even though it grows like a weed and has nasty prickles, this low-growing woody vine is native to North America and has some good points. The fruits are a food source for many bird species. After eating the fruits, they scatter them all over our land, which is why the plants seem to appear out of nowhere.

Other plants, like horsenettle (Solanum carolinense), have prickles on both stems and leaves. Horsenettle is a bothersome weed that occurs both in pasture fields and in home landscapes. There are prickles on the stems, petioles, leaf veins, and even the flower stalks of this plant. Because the plant is so prickly, animals are deterred from grazing. It turns out that this is a good thing because the plants and their fruits can hurt animals.

For yet other plant species, the prickles are attached at the base of the leaves only. Spiny amaranth (Amaranthus spinosus) is one such example. The very sharp, stiff prickles on this plant can be as long as a quarter of an inch. Also, a fully grown spiny amaranth plant can make around 235,000 seeds, which makes it a tough weed to get rid of.

A few plants have reflexed or recurved prickles, meaning that the tips point downward. This design hinders small animals from climbing stems to reach leaves on some plants. On some plants, especially ones with long stems, the prickles make it possible for the plant to attach itself to other plants or branches for support. A plant with reflexed prickles is Mile-a-minute vine (Persicaria perfoliata), which is very invasive and hard to get rid of.

MORE PRICKLY PLANT STRUCTURES

There are a lot of plants with prickly personalities that don’t fit neatly into the three groups we just talked about. A few variations on a theme include the following.

Sticky parts on flower heads, seeds, or fruits—These kinds of structures make a lot of sense from an evolutionary point of view. For their species to stay alive, plants need to spread their seeds to new places where they will have less competition for food, water, and light. One very effective way for seeds to get to other places is to use special mechanisms that look like barbs and are made to help the seeds stick to things or hitchhike. According to Botany for Gardeners by Brian Capon, “hooks and barbs are a reliable sign that a seed or fruit is ready to hitch a ride on a passing animal.” ”.

Here are a few examples of weeds equipped for hitchhiking:

• Beggarticks (Bidens bipinnata): The dark brown, long seeds have tiny barbs on them that are meant to stick to clothing and animal fur. This is the weed that I found to be the problem in my perennial garden.
• Cleavers or Catchweed bedstraw (Galium aparine): The tiny, round fruits have very short, curved hooks on them and are spread by animals eating them or floating on water.
• This weed is called Prickly Sida or Spiny Sida (Sida Spinosa), and each leaf and branch has a very small prickle at the base of it. The circular seedpods have five segments that break apart. Each part has two spikes or protrusions that look like beaks on the end.
• Sticktights, also known as Seed Ticks (Desmodium species)—The flat, triangular seeds stick to animal fur or clothing with the help of small, barbed hairs that give the seeds a fuzzy look.

Many plants have fine hairs or bristles that protect them from heat or cold and from herbivores, among other things. Prickly lettuce (Latuca serriola) is such a plant. The edges of these weed’s leaves are sharp, and there is a row of stiff, sharp bristles on the lower midvein. Between the prickly leaves and milky sap, this is not a pleasant plant. It is also quite prolific. According to Weeds of North America, a large, mature plant can produce up to 87,000 seeds!.

Burs: A bur, which is sometimes spelled burr, is a seed or dry fruit with hooks or teeth that are meant to keep herbivores away and spread seeds by sticking to fur or clothing. Depending on the plant species, burs can be a mild annoyance or a serious hazard. On the annoying side, they can snag or tear one’s clothing. Some burs are very dangerous because they can puncture tires, catch on animals’ legs or feet and hurt them, and damage farming tools used for harvesting.

Some plants with burs include the following:

• Common Burdock (Arctium): This big, rough-looking biennial weed blooms in late summer with pollen and nectar that bees and some Lepidoptera species can use. Plus, this plant is what made people think of the hook-and-loop fastener called Velcro. The plant does have a lot of burs that can get caught on fur or clothing and be painful to pull out.
• That’s the Common Cocklebur (Xanthium strumarium). It has hard, woody burs that are covered in hooked prickles and have two long beaks that stick out from the end of the bur. The burs can float on water and stick to clothing or animal fur.
• Jimson Weed (Datura stramonium): This big weedy plant has funnel-shaped flowers that open at night and feed nocturnal moths pollen. The leaves look like they have spines, and the big seed pods look like they have spikes on them. All plant parts are poisonous.
• Teasel (Dipsacus fullonum): This non-native plant is very competitive with other plants for space and food, so it is thought to be invasive. The oval-shaped, spiny seed heads that look like evil grow on long, prickly stalks. The teasel plant makes about 2,000 seeds per plant and can be found in disturbed areas, pastures, and along roadways.

ET TU, VEGGIES?

Yes, even vegetables have their share of prickly personalities. For example, some types of eggplant have small spikes on their stems and on the calyx, which is where the fruit meets the stem. Grasping the stem at that point with bare hands can be painful. When you touch yellow squash plants with your bare hands, the stems and leaves can be painfully sharp. Even the fruits are covered with fine, nearly transparent hair-like bristles. Some, but not all, cucumber varieties have slightly spiny fruits as well as prickly stems. Artichokes have prickly leaves and beautiful violet-purple thistle-like flowers that attract pollinating insects. The flower bud that can be eaten has scale-like leaves with short, poisonous thorns on the ends that must be cut off.

PREVENTION/CONTROL OF PRICKLY PLANTS

Except for the vegetables, many of the prickly plants described herein are opportunists. They appear most often in disturbed soil, such as alongside roadways, construction sites, or garden beds. Beyond being blown around by the wind or carried by water, wild animals, birds, people, and our pets can also spread seeds. It’s important to get rid of the plants when they are seedlings for several reasons, no matter how they are spread:

• When it first comes up from the ground, a seedling is easier to handle than when it is fully grown.
• A lot of these plants have tap roots that are easier to pull out of the ground when they are small.
• Many of these plants make huge amounts of seeds, which should be gotten rid of before they sprout.

THE TAKEAWAY….

If you change a thorn into a spine, you change a leaf or part of a leaf into a thorn. A prickle is an outgrowth from the epidermal tissue of stems, leaves, and some fruits. You don’t need to know the differences between these three unless you want to use that information to help you identify plant species. Keep in mind that not all plants with sharp or prickly outgrowths are weeds or even undesirable. Many of these plant species are valuable sources of pollen, nectar or shelter for pollinators and other wildlife. But it is important to figure out which plants aren’t wanted and should be gotten rid of before they become a problem. The best things you can do are stop them from planting seeds in the first place or get rid of them when they are seedlings.

As I think about the Beggar’s weed that led me to this discovery, I now understand and even admire how it stays alive. The plant is rooted in the soil and cannot move. That’s why, many thousands of years ago, its ancestors learned how to use moving things to spread their seeds. There’s even a term for this strategy: zoochory. Pretty clever, don’t you think?.

Featured photo: Common thistle armed with formidable prickles on stems, leaves and flowers. Photo: Pat Chadwick

SOURCES:

Botany for Gardeners, Third edition (Capon, Brian, 2010)

Weeds of the Northeast, (Uva, Richard, Neal, Joseph C., and DiTomaso, Joseph M., 1997)

Weeds of North America (Dickinson, Richard and Royer, France, 2014), The University of Chicago Press

Virginia Weed Identification, Virginia Tech website Start – Weed Identification (vt.edu)

University of Missouri Weed ID guide, https://weedid.missouri.edu/

“Identification of Virginia’s Noxious Weeds,” Virginia Cooperative Extension Publication SPES-244NP https://www.vdacs.virginia.gov/pdf/va_noxious_weeds.pdf

Botany 115 Vegetative Terminology, Modified Roots, Stems and Leaves

Of Thorns, Spines and Prickles, University of Missouri Integrated Pest Management article by David Trinklein, published January 3, 2013.

Many plant species worldwide are armed with thorns, spines, prickles, and other hazardous outgrowths. But why?

The November To-Do List

In the Edible Garden

Explore winter squash and discover how to grow and enjoy this versatile, highly nutritious garden produce

It’s time to close up the vegetable garden for the winter and start doing things that will help it come spring.

In the Ornamental Garden

Are there some resilient enough for climate change?

Recipe of the Month

As American as apple pie

Opuntia for FREE! – How to plant & propagate Prickly Pear Cactus

FAQ

What is the prickle on a plant called?

What is a thorn or spike on a plant?

What is a prickly plant called?

What is another word for prickly plant crossword clue?

What is a prickly plant?

Spines are modified leaves. Prickles are epidermal appendages without vascular connections. Sharp protrusions help defend plants, reduce water loss, and anchor climbing vines. Hooks and barbs on seeds enable dispersal via attachment to passing animals. Some prickly plants provide essential food and habitat for pollinators and other wildlife.

What is a prickle in a plant?

These marginal spines are extensions of the leaf’s major veins. Having spines at the very end—Some plants, like Agave, Sansevieria, and Yucca species, have sharp points (called terminal spines) on the ends of their leaves. Prickles are short, sharp, woody projections that come from the epidermis tissue of a plant.

Are prickly plants weeds?

It’s easy to assume prickly plants are troublesome weeds. However, the sharp structures serve a purpose, whether for protection, climbing support, or seed dispersal. Many prickly plants provide food and habitat for wildlife. For example: Thistles – Nectar and pollen attract bees and butterflies. Prickly poppies – Seeds feed small mammals and birds.

What are thorns and prickles in plant morphology?

In plant morphology, thorns, spines, and prickles, and in general spinose structures (sometimes called spinose teeth or spinose apical processes), are hard, rigid extensions or modifications of leaves, roots, stems, or buds with sharp, stiff ends, and generally serve the same function: physically defending plants against herbivory.

What do prickly plants eat?

Many prickly plants provide food and habitat for wildlife. For example: Thistles – Nectar and pollen attract bees and butterflies. Prickly poppies – Seeds feed small mammals and birds. Greenbrier – Fruits eaten by birds, dispersed in droppings. Evaluate prickly plants individually before removing them.

Why do prickly plants need hooks and barbs?

Hooks and barbs on seeds enable dispersal via attachment to passing animals. Some prickly plants provide essential food and habitat for pollinators and other wildlife. It’s important to properly identify and manage prickly plants rather than automatically removing anything perceived as a nuisance.