Carolina Horsenettle - Weed or Wildflower?

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.

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.

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 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.

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.