Carolina Horsenettle - Weed or Wildflower?

by cazort

The Carolina horsenettle, Solanum carolinense, is often viewed as a noxious weed, but it can also be seen as a native wildflower of prairie habitats.

The Carolina horsenettle, Solanum carolinense, is often viewed as a noxious weed. It even has obtained unflattering-sounding names such as "apple of Sodom", "bull nettle", and "devil's tomato".

It is covered in spines, and the leaves and stems are toxic not only to humans, but to most mammals.

But is this plant all bad? Below we discuss how this plant is much maligned: its weedy behavior is often a result of human interventions, and in its natural habitat, it maintains a balance with other species, and contributes to a healthy ecosystem. This page will teach you more about this plant, explaining how, when, and where it becomes a weed, and how both to control it, and to integrate it into a garden or ecosystem in a more balanced manner.

A Nightshade, Not a True Nettle

Not stinging, not edible--just spiny and toxic

Solanum carolinense is not a nettle as its name suggests, but rather, a nightshade.  This is an important distinction--true nettles are covered in stinging hairs, but are also edible if cooked.  The Carolina horsenettle, by contrast, is thorny but not stinging, and is poisonous to eat.

Native to North America, but considered invasive in some areas

Native to North America; has expanded its range north into Canada through disturbed habitats created by human intervention

Solanum carolinense has a wide native range, across most of the lower 48 states.  Its range has expanded somewhat though due to human activity, and it is considered invasive at the northernmost limit of its range, in Canada.

Two Carolina horsenettles growing in a flower bed
Two Carolina horsenettles growing in a flower bed
Photo by Alex Zorach

Identification: What to Look For

How to distinguish from similar-looking plants

The Carolina horsenettle is relatively easy to identify among its nightshade relatives.  Its growth habit looks a lot like that of an eggplant, one of its close relatives, and it also resembles plants of the Datura genus, like Jimsonweed and Angel's trumpet.  But unlike all these plants, it is covered in thorns, which cover both its stem, and the larger veins of leaves.

The flower is also distinctive, relatively small but showy, with white petals and bright yellow stamens in a five-pointed star shape.  It looks a little like eggplant flowers, but is all-white with a yellow center.  Eggplant flowers usually are pink or at least have pink tinges, and the Datura sp. have huge, trumpet-shaped flowers.

In most parts of the U.S., it is the only common plant fitting this description, but in Florida, it could possibly be confused with Solanum capsicoides, another thorny (and also poisonous) plant of the same genus.  That plant has different-shaped leaves, deeply lobed, almost shaped more like an oak leaf, and much larger.  In the west and center of the country, the buffalobur nightshade, Solanum rostratum, is another thorny nightshade, but there is little risk of confusion: this plant has deeply lobed leaves and solid yellow flowers.

The Spines and Flower Can Be Used for Quick ID

No other nightshade with similarly shaped leaves also has thorns; in most of its range it is the only nightshade with thorny stems. Also, the flower is distinctive.
Closeup Showing Spines and Flower
Closeup Showing Spines and Flower
Photo by Alex Zorach

Toxic Stems and Leaves...

...just like tomato, potato, eggplant, and both sweet and hot peppers.

The Carolina horsenettle, like most members of the Solanum genus, has stems and leaves that are toxic, not only to humans, but to most mammals.  The plant contains a variety of poisonous alkaloids, including solanidine.  Doesn't sound like the sort of thing you would want in your garden, right?

Would you be surprised to know that many food plants, including tomato, potato, and eggplant, are in the same genus as this plant, Solanum, and that their leaves and stems also contain toxic alkaloids?  Yes, and peppers (both sweet peppers and hot peppers) are in the same family, Solanaceae, and also have toxic foliage.  It is only the fruit of tomato, eggplant, and peppers, and the tubers of potato, that are edible.

The toxicity of these food plants' foliage may actually be an asset to humans, because it discourages or prevents animals like deer and rabbit from eating the leaves.

Habitat and Growing Requirements

Human disturbance of ground, and use of insecticides, tends to make this plant more weedy and aggressive.

The Carolina horsenettle prefers full sun, and can grow in both moist and dry conditions.  It is not particularly picky about soil type, and can grow well in sandy soil.

It thrives most in disturbed habitats, such as roadsides, along railroad tracks, in vacant lots, and exposed beds in yards and gardens.  In these disturbed habitats, it has to deal with less competition from other plants, and often becomes very weedy and aggressive, and hard to control.

In wild ecosystems, both insect herbivores and competition from other plants keep this plant in check.

The insects that eat this plant are diverse, and include a beetle specialized on this particular species, the false potato beetle, which prefers this plant over the cultivated food nightshades, and is not a serious pest of food crops, unlike the Colorado potato beetle.  In the wild, the natural herbivores of this plant do enough damage to it that its growth and reproduction is significantly slowed.  The widespread use of insecticides in an area will thus tend to favor horsenettle.

This plant attracts bumblebees

Bumblebees are the main pollinators of the flowers of this plant.
Bumblebee on a Horsenettle Flower
Bumblebee on a Horsenettle Flower
Photo by Alex Zorach

The False Potato Beetle

The Carolina horsenettle is the preferred host of this beetle, which specializes on eating the foliage of this plant.
Larvae of False Potato Beetle on Carolina Horsenettle
Larvae of False Potato Beetle on Carolina Horsenettle
False Potato Beetle, Adult
False Potato Beetle, Adult

What do you think? Weed or Wildflower?

Updated: 03/17/2015, cazort
 
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frankbeswick on 06/14/2016

How did I miss this article when it came out? Yet another informative piece from you, Cazort! It raises the important issue that popular names are a poor guide to botanical classification [horse nettle not being a nettle.] I can learn about American botany from your articles, and that's useful, because we don't have American flora where I live.

cazort on 06/14/2016

That's fascinating about the goats. Goats are definitely able to eat a wide variety of plants that are poisonous to humans, or in some cases, they're able to eat much larger quantities than we would be able to, without adverse effects.

Animals definitely do practice their own form of "herbalism". For example, some species of swallow gather herbs that have insecticidal properties, and place them in their nest, and then this reduces the prevalence of mite infestations in their nests. It makes sense that mammals would develop the ability to respond to parasites by eating things that would kill the parasites.

If you think about it, humans actually eat a lot of "toxic" stuff that we are evolved to be able to tolerate, like the whole garlic and onion family, those are poisonous to a lot of animals and microorganisms, but we can eat them--and then the chemicals accumulate in our bodies (like how you can smell it on someone if they've eaten a lot of garlic). And garlic is really effective at killing microorganisms. It seems pretty widespread in animals, that specific animals will develop the ability to eat specific toxic plants while tolerate the toxins, then accumulating them in their own systems in ways that benefits them. Another example is monarchs or lightning bugs that eat bitter plants so that birds will learn they taste unappealing, and thus avoid eating them.

Jason Ellis on 11/08/2015

This nightshade looks look very similar to one we have here in Texas and at first glance I thought it was Silverleaf Nightshade (Solanum elaeagnifolium). I've read that different Native American tribes used seeds from the Silverleaf Nightshade as a vegetable rennet to curdle milk and make cheese.

Amanda - I've owned goats and I believe they're animal herbalists. Whenever my goats encountered a plant they didn't know they would brush their faces against it, sniff it, perhaps nibble but never eat it. The next time they would eat a little. The following time they would eat a lot. At least this is what they appeared to do and it follows a similar method human survivalists use to check the edibility of food!

Amanda on 07/10/2015

Hi there: thought you might be interested to know that, contrary to everything I have read about Carolina Horsenettle, it has actually served as forage for my goats this spring. I also spent the day at a friend's ranch today and saw that his sheep have also been consuming it. Neither group of livestock was put in a situation where they HAD to consume this plant--they chose it over other plants that were readily available! I am often mystified by my goats' food choices, but trust that there is a good reason they're munching these leaves (natural worm/parasite control? high concentrations of trace minerals?) and we just have yet to learn why. Thanks for this article--I enjoyed it!

cazort on 09/07/2014

Thank you! I agree.

I also think it is a little silly to view this plant as a weed--it does not compete very well with other plants, and when it has cropped up in my garden, it's generally only grown in open spaces. When I plant other flowers, even sun-loving flowers like goldenrod will out-compete it. It's one of those plants that only really thrives if you keep pulling out weeds and leaving open spaces in your garden.

DerdriuMarriner on 09/06/2014

cazort, Well done! It's especially helpful that you explain visible differences between Carolina horsenettle and other nightshades.
Carolina horsenettle numbers among those plants which generate controversy over the welcomeness vs unwelcomeness of their appearance in the landscape.
I'm inclined to agree with the bees: this plant has value, a value appreciated by bees but unknown to or forgotten by people.

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